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This Mushroom & Spinach Gratin is the kind of side dish that makes you want one more bite. Earthy mushrooms, tender spinach, and sweet caramelized shallots are tucked into a creamy cheesy sauce and baked until golden and bubbling. It’s cozy, comforting, and just fancy enough to steal the spotlight at your next dinner.
Table of Contents
I am an absolute sucker for creamed spinach. Pair it with mashed potatoes and steak, and I am one happy woman. But add mushrooms, caramelize some shallots, and top it with melty cheese? I am in heaven. I had to stop myself from eating it straight from the dish! This creamy mushroom & spinach gratin dish is one of the best dishes I’ve made. It’s definitely one of the must-have Thanksgiving side dishes to impress others.
Why You’ll Love This Recipe
This gratin is creamy, cheesy, cozy, slightly sweet, and savory. It’s the perfect dish! The caramelized shallots add a subtle sweetness that balances the earthy mushrooms and spinach beautifully. It’s absolutely irresistible with the shallots on top. It’s also a great way to get your veggies! It transforms into a creamy spinach & mushroom gratin when you add gooey, melted Gruyère cheese. You might be tempted to eat this for dinner by itself one night, but you should definitely pair this with proteins. Serve this with turkey for Thanksgiving, or on a weekday, serve it with chicken, steak, pork, or salmon.
Ingredients for Mushroom & Spinach Gratin with Caramelized Shallots
- Frozen Spinach: Frozen spinach is such an easy ingredient for everyday cooking. When you are defrosting this, make sure you squeeze out as much liquid as possible. Water is a cream sauce’s enemy.
- Mushrooms, Yellow Onions, Garlic: I used white button mushrooms. You can use baby bella (or cremini, as it’s also called) if you wish.
- Shallots, Sugar, Salt, Butter: The ingredients to make the caramelized shallots. You will need a lot of shallots. When they caramelize, they shrink so fast. Luckily, shallots do not cost that much per pound so it won’t break the bank.
- Whole Milk, Heavy Cream: The cream base for the gratin. You can sub the heavy cream for half and half or 4 oz of cream cheese. If you’re looking for dairy-free options, unsweetened coconut cream works in place of heavy cream, and unsweetened plant milk works in place of the regular milk.
- All-Purpose Flour & Nutmeg: Trust me, do not skip the nutmeg. It’s a great ingredient for cream-based dishes such as this one. It only adds a subtle flavor that brings out the savoriness.
- Shredded Gruyère & Parmesan Cheese: The cheesy part of the gratin. Half of the Parmesan goes into the creamy spinach mushrooms, and the other half is sprinkled on top with the Gruyère.
Tips & FAQs
- Storage: Allow to cool completely, then store in an airtight container in the fridge for up to 4 days. If you store it straight in the baking dish (which I did), I recommend reheating in a 350F degree oven until completely reheated. If the cheese starts browning too much, then cover loosely with foil and reheat that way.
- Make Ahead: Assemble everything the day before serving. Cover tightly with foil or plastic wrap until you’re ready to bake it. Let it sit at room temperature for at least 30 minutes before baking it. You may need to add another 5-10 minutes to the baking time. If the cheese starts browning too much, then cover loosely with foil and bake that way.
- I don’t recommend freezing it. The gratin might get mushy and may separate because of the cream.
- Can I use fresh spinach? Absolutely! You will need a lot of fresh spinach if you want to achieve the same result. 5 lbs of spinach will be an equal amount. Blanch the spinach in boiling water for only a minute or two, cool slightly, and squeeze out any excess water. Chop the spinach before adding to the creamy mushroom sauce.
- What to Serve With This: It’s delicious alongside a holiday roast dinner. If you’re making this on a normal day, then I would serve a simple roasted protein. Chicken, steak, pork tenderloin, or salmon are great options. Don’t forget the dinner rolls to mop up the gratin with!
- Variations:
- Change up the cheese with fontina, Swiss, or a combination.
- Crisp up some panko breadcrumbs, then add them on top of the cheese for a crunchy element,
- Make it heartier by adding crispy bacon, pancetta, or crumbled sweet Italian sausage.
- Switch the spinach out for kale or Swiss chard. Make sure you cook them until tender before adding them to the gratin.
- Add some herbs like thyme, parsley, or oregano to this. If you have any leftover herbs from your roast dinner, feel free to add them.
- Give it some heat by adding crushed red pepper flakes or a dash of hot sauce.
- Wine Pairings:
- A Chardonnay complements this creamy spinach and mushroom gratin so well. Find one that’s buttery and lightly oaked.
- If you want a red for this, a Pinot Noir is the way to go. It has a bright acidity and an earthy character, making this a natural match with the spinach and mushrooms.
- Looking for something different? Try a dry Riesling. The acidity keeps the dish from feeling too heavy and provides a refreshing contrast to the creamy sauce.
- For Non-Alcoholic Options: Pair this with a sparkling apple cider, which is my absolute favorite holiday drink of choice. A secondary pairing is a classic sparkling water with lemon in it. Looking for a mock prosecco? Mix white grape juice with sparkling water for a lightly sweet pairing that mirrors the prosecco.
Recipe:
Mushroom & Spinach Gratin with Caramelized Shallots
This Mushroom & Spinach Gratin is the kind of side dish that makes you want one more bite. Earthy mushrooms, tender spinach, and sweet caramelized shallots are tucked into a creamy, cheesy sauce and baked until golden and bubbling. It’s cozy, comforting, and just fancy enough to steal the spotlight at your next dinner.
Ingredients
Caramelized Shallots
- 6 tbsp unsalted butter
- 10 medium shallots peeled and sliced
- 2 tbsp sugar
- 2 tsp salt
Mushroom & Spinach Gratin
- 4 tbsp unsalted butter
- 20 oz white button or baby bella mushrooms stems trimmed and sliced 1/4-inch thick
- 1 medium yellow onion chopped, about 1 1/2 – 2 cups
- 2 garlic cloves minced
- Salt & pepper to taste
- ¼ cup all-purpose flour
- ¼ tsp ground nutmeg
- 2 cups whole or 2% milk
- 1 cup heavy cream
- 4 10 oz packages frozen spinach thawed completely and drained of all excess liquid
- 1 cup grated parmesan cheese divided
- ½ cup shredded gruyere cheese
Instructions
- Preheat the oven to 425F. Grease a 9×13 baking dish.
For Caramelized Shallots:
- Melt 6 tbsp of butter in a medium sauté pan over medium heat. Once melted, add the shallots and cook for 5 minutes until it starts cooking down. Sprinkle them with the sugar and salt.
- Lower the heat to medium-low. Cook until caramelized, about 10 minutes. Remove from heat and set aside in a bowl.
For the Gratin:
- Melt 4 tbsp of butter in a large skillet over medium-high heat. Add the mushrooms and onions, season with a little salt, and sauté until the onions are translucent and the mushroom's liquid evaporates and have browned a bit, about 15 minutes. Stir in the garlic and cook for 1-2 minutes more until aromatic.
- Lower the heat to medium. Sprinkle in the flour and nutmeg. Stir to coat the mushroom mixture. Cook for 2 minutes until the flour is toasted. Whisk in the milk and heavy cream. Let it simmer gently until thickened, whisking often, about 6-7 minutes. Remove from the heat completely. Season with salt and pepper as needed.
- Squeeze out any excess liquid from the spinach as possible, then add to the sauce along with 1/2 cup of parmesan cheese. Stir it all in, breaking up the spinach so it thoroughly mixes in. Season with salt and pepper as needed.
- Transfer the spinach mixture to the greased 9×13 baking dish and spread evenly. Distribute the caramelized shallots on top, then sprinkle the gruyere and parmesan on top evenly.
- Bake, uncovered, for 20 minutes until hot and bubbly and the cheese has melted. If the cheese is browning quickly, then cover it loosely with foil. Serve immediately.
Notes
- Storage: Allow to cool completely, then store in an airtight container in the fridge for up to 4 days. If you store it straight in the baking dish (which I did), then I recommend reheating this in a 350F degree oven until completely reheated. If the cheese starts browning too much, then cover loosely with foil and reheat that way.
- Make Ahead: Assemble everything the day before serving. Cover it tightly with foil or plastic wrap until you’re ready to bake it. Let it sit at room temperature for at least 30 minutes before baking it. You may need to add another 5-10 minutes to the baking time. If the cheese starts browning too much, then cover loosely with foil and bake that way.
- I don’t recommend freezing it. The gratin might have a mushy texture and may separate because of the cream.
- Can I use fresh spinach? Absolutely! You will need a lot of fresh spinach if you want to achieve the same result. 5 lbs of spinach will be an equal amount. Blanch the spinach in boiling water for only a minute or two, cool slightly, and squeeze out any excess water. Chop the spinach before adding to the creamy mushroom sauce.
- Can I use dairy-free milk & cream? You can sub the heavy cream for half and half or 4 oz of cream cheese. If you’re looking for dairy-free options, unsweetened coconut cream works in place of heavy cream, and unsweetened plant milk works in place of the regular milk.
- What to Serve With This: It’s delicious alongside a holiday roast dinner. If you’re making this on a normal day, then I would serve a simple roasted protein. Chicken, steak, pork tenderloin, or salmon are great options. Don’t forget the dinner rolls to mop up the gratin with!
- Variations:
- Change up the cheese with fontina, Swiss, or a combination.
- Crisp up some panko breadcrumbs, then add them on top of the cheese for a crunchy element,
- Make it heartier by adding crispy bacon, pancetta, or crumbled sweet Italian sausage.
- Switch the spinach out for kale or Swiss chard. Make sure you cook them until tender before adding them to the gratin.
- Add some herbs like thyme, parsley, or oregano to this. If you have any leftover herbs from your roast dinner, feel free to add them.
- Give it some heat by adding crushed red pepper flakes or a dash of hot sauce.
-
Wine Pairings:
- A Chardonnay complements this so well. Find one that’s buttery and lightly oaked.
- If you want a red for this, a Pinot Noir is the way to go. It has a bright acidity and an earthy character, making this a natural match with the spinach and mushrooms.
- Looking for something different? Try a dry Riesling. The acidity keeps the dish from feeling too heavy and provides a refreshing contrast to the creamy sauce.
- For Non-Alcoholic Options: Pair this with a sparkling apple cider, which is my absolute favorite holiday drink of choice. A secondary pairing is a classic sparkling water with lemon in it. Looking for a mock prosecco? Mix white grape juice with sparkling water for a lightly sweet pairing that mirrors the prosecco.
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