Creamy Asparagus and Mushroom Gratin

I didn’t grow up eating a lot of fancy casseroles, but gratins always felt special to me. Maybe it was the bubbly cheese on top or the way everything baked together in one dish. Either way, they were reserved for company or holidays.

This asparagus and mushroom gratin changed that for me. It’s the kind of recipe that looks like you worked hard but really didn’t. You just make a simple sauce, toss in your veggies, top it with cheese, and let the oven do its thing. The sherry adds something extra—a little grown-up flavor that makes it taste restaurant-worthy. But here’s the best part: it’s a great way to get vegetables on the table without anyone complaining.

What Kind of Mushrooms Should I Use?

For this gratin, you have plenty of options when it comes to mushrooms. White button mushrooms are the most budget-friendly choice and work perfectly fine, while cremini mushrooms (also called baby bellas) will give you a slightly deeper, earthier flavor. If you want to get a bit fancier, shiitake or a mix of wild mushrooms can add some really nice complexity to the dish. Whatever you choose, make sure to clean them gently with a damp paper towel rather than rinsing them under water, since mushrooms absorb moisture like a sponge and can get soggy. Slice them about 1/4-inch thick so they cook evenly and release their moisture properly during baking.

Options for Substitutions

This gratin is pretty forgiving when it comes to swaps, so here are some options if you need them:

• Asparagus: Green beans or broccoli florets make great substitutes. Just blanch them the same way you would the asparagus to keep them tender-crisp.
• Mushrooms: Any mushroom variety works here – button, cremini, shiitake, or even a mix. You could also add extra asparagus instead if mushrooms aren’t your thing.
• Sherry: Don’t have sherry on hand? Try white wine, dry vermouth, or even a splash of chicken broth with a tiny bit of lemon juice for that hint of acidity.
• Mozzarella: Gruyere, fontina, or white cheddar all melt beautifully in this dish. You can also use a combination of cheeses – just keep the total amount at 1 cup.
• Milk: Whole milk works best for a creamy sauce, but you can use 2% if that’s what you have. For a richer gratin, swap half the milk with heavy cream.
• Butter and flour: These create the roux base for your sauce, so I wouldn’t recommend skipping them. They’re what makes the sauce thick and creamy.

Watch Out for These Mistakes While Cooking

The biggest mistake people make with this gratin is not cooking the asparagus before baking, which can leave you with crunchy, undercooked spears – blanch them in boiling water for 2-3 minutes first, then drain well to avoid a watery casserole.

When making the sauce, adding the milk too quickly can create lumps in your roux, so pour it in gradually while whisking constantly to get that smooth, creamy texture.

Another common error is overcrowding the mushrooms in the skillet, which causes them to steam instead of brown – cook them in batches if needed and make sure to let their moisture evaporate completely before adding them to the dish.

Finally, don’t skip letting the gratin rest for 5-10 minutes after baking, as this helps the sauce thicken up and makes serving much cleaner.

What to Serve With Asparagus and Mushroom Gratin?

This gratin makes a great side dish for just about any protein you’re cooking up for dinner. I love serving it alongside roasted chicken, grilled steak, or even pan-seared pork chops since the creamy, cheesy sauce pairs nicely with simple meats. If you want to make it the star of the meal, add a fresh garden salad and some crusty bread to round things out. The gratin also works well as part of a bigger spread for holidays or potlucks, sitting right next to other veggie sides or a big bowl of mashed potatoes.

Storage Instructions

Store: Keep any leftover gratin covered tightly with foil or in an airtight container in the fridge for up to 3 days. The asparagus will soften a bit more as it sits, but the flavors actually get better overnight as everything melds together.

Make Ahead: You can assemble this gratin up to a day before baking. Just prep everything through the sauce and cheese layer, cover it well, and refrigerate. When you’re ready to serve, let it sit at room temperature for about 20 minutes, then bake as directed, adding an extra 5-10 minutes if needed.

Reheat: Warm up leftovers in a 350°F oven covered with foil for about 15-20 minutes until heated through. You can also microwave individual portions for 1-2 minutes, though the oven method keeps the top a bit crispier.

Estimated Nutrition

Estimated nutrition for the whole recipe (without optional ingredients):

• Calories: 1250-1400
• Protein: 40-48 g
• Fat: 75-90 g
• Carbohydrates: 90-105 g

Ingredients

For the vegetables:

• 2.5 lb asparagus (tough ends trimmed and cut into 2-inch pieces)
• 8 oz mushrooms (sliced into 1/4-inch thick pieces)
• 1 tbsp butter

For the sauce:

• 1/4 cup butter (I like Kerrygold unsalted butter for this)
• 1/4 cup flour (I always use King Arthur all-purpose flour)
• 2 cups milk
• 3 tbsp sherry (dry variety adds a sophisticated depth of flavor)
• 1 cup mozzarella
• 1/4 tsp salt
• 1/4 tsp pepper
• 1/4 tsp garlic powder

Step 1: Prepare the Vegetables

• 2.5 lb asparagus
• 8 oz mushrooms

Trim the tough woody ends from the asparagus and cut the spears into 2-inch pieces.

Slice the mushrooms into 1/4-inch thick pieces.

Having both vegetables prepped and ready will allow you to work efficiently once you start cooking.

Step 2: Sauté the Mushrooms

• 1 tbsp butter
• 8 oz mushrooms

Melt 1 tablespoon of butter in a large skillet over medium-high heat.

Add the sliced mushrooms and sauté for about 5 minutes, stirring occasionally, until they release their moisture and begin to lightly brown.

This develops their savory flavor before they join the gratin.

Set the cooked mushrooms aside on a plate.

Step 3: Build the Béchamel Sauce

• 1/4 cup butter
• 1/4 cup flour
• 2 cups milk
• 3 tbsp sherry
• 1 cup mozzarella
• 1/4 tsp salt
• 1/4 tsp pepper
• 1/4 tsp garlic powder

Melt 1/4 cup butter in a saucepan over medium heat.

Once melted, whisk in the flour to create a paste, stirring constantly for about 1 minute to cook out the raw flour taste.

Gradually pour in the milk while whisking to prevent lumps from forming.

Continue cooking and stirring until the sauce thickens, about 3-4 minutes.

The sauce should coat the back of a spoon when ready.

Remove from heat and stir in the dry sherry, mozzarella cheese, salt, pepper, and garlic powder until the cheese melts completely and the sauce is smooth.

Step 4: Preheat Oven and Assemble the Gratin

• 2.5 lb asparagus
• 8 oz mushrooms

While the sauce finishes cooking, preheat your oven to 350°F and lightly butter a 9×13-inch baking dish (or similar size).

Once the oven is ready, spread the prepared asparagus pieces evenly across the bottom of the dish.

I find that spreading the asparagus in a relatively even layer helps it cook more uniformly.

Scatter the sautéed mushrooms from Step 2 over the asparagus.

Step 5: Combine and Bake

• béchamel sauce from Step 3
• asparagus and mushroom mixture from Step 4

Pour the béchamel sauce from Step 3 evenly over the asparagus and mushroom mixture, making sure to coat the vegetables well.

Bake in the preheated 350°F oven for 30 minutes, until the sauce is bubbling around the edges and the top is lightly golden.

The gratin is ready when the vegetables are tender and the sauce has reduced slightly into a creamy coating.

Creamy Asparagus and Mushroom Gratin

Delicious Creamy Asparagus and Mushroom Gratin recipe with step-by-step instructions.

Print Recipe Pin Recipe

Prep Time 15 minutes mins

Cook Time 35 minutes mins

Total Time 50 minutes mins

Servings 6 servings

Calories 1325 kcal

Ingredients

  

For the vegetables

• 2.5 lb asparagus (tough ends trimmed and cut into 2-inch pieces)
• 8 oz mushrooms (sliced into 1/4-inch thick pieces)
• 1 tbsp butter

For the sauce

• 1/4 cup butter (I like Kerrygold unsalted butter for this)
• 1/4 cup flour (I always use King Arthur all-purpose flour)
• 2 cups milk
• 3 tbsp sherry (dry variety adds a sophisticated depth of flavor)
• 1 cup mozzarella
• 1/4 tsp salt
• 1/4 tsp pepper
• 1/4 tsp garlic powder

Instructions

 

• Trim the tough woody ends from the asparagus and cut the spears into 2-inch pieces. Slice the mushrooms into 1/4-inch thick pieces. Having both vegetables prepped and ready will allow you to work efficiently once you start cooking.
• Melt 1 tablespoon of butter in a large skillet over medium-high heat. Add the sliced mushrooms and sauté for about 5 minutes, stirring occasionally, until they release their moisture and begin to lightly brown. This develops their savory flavor before they join the gratin. Set the cooked mushrooms aside on a plate.
• Melt 1/4 cup butter in a saucepan over medium heat. Once melted, whisk in the flour to create a paste, stirring constantly for about 1 minute to cook out the raw flour taste. Gradually pour in the milk while whisking to prevent lumps from forming. Continue cooking and stirring until the sauce thickens, about 3-4 minutes. The sauce should coat the back of a spoon when ready. Remove from heat and stir in the dry sherry, mozzarella cheese, salt, pepper, and garlic powder until the cheese melts completely and the sauce is smooth.
• While the sauce finishes cooking, preheat your oven to 350°F and lightly butter a 9x13-inch baking dish (or similar size). Once the oven is ready, spread the prepared asparagus pieces evenly across the bottom of the dish. I find that spreading the asparagus in a relatively even layer helps it cook more uniformly. Scatter the sautéed mushrooms from Step 2 over the asparagus.
• Pour the béchamel sauce from Step 3 evenly over the asparagus and mushroom mixture, making sure to coat the vegetables well. Bake in the preheated 350°F oven for 30 minutes, until the sauce is bubbling around the edges and the top is lightly golden. The gratin is ready when the vegetables are tender and the sauce has reduced slightly into a creamy coating.