Name: Baked Mushroom and Zucchini Gratin
Prep time: 20 min
Cook time: 40 min
Total time: 1 h 10 min
Yield: 6
Cuisine: French
Ingredients: 4 medium zucchini (about 2 lbs / 900g), sliced into ¼-inch rounds; 1 lb (450g) cremini or button mushrooms, sliced; 1 medium onion, thinly sliced; 3 cloves garlic, minced; 1½ cups (360 ml) heavy cream; ½ cup (120 ml) whole milk; 1½ cups (150g) grated Gruyère cheese (or Swiss/Comté); ½ cup (50g) grated Parmesan cheese; ¾ cup (75g) panko breadcrumbs; 3 Tbsp butter, divided (2 Tbsp melted for topping); 2 Tbsp all-purpose flour; 1½ tsp fresh thyme leaves (or ½ tsp dried); ½ tsp ground nutmeg (optional); Salt and freshly ground black pepper, to taste; Olive oil, for sautéing

This creamy Baked Mushroom and Zucchini Gratin layers tender zucchini slices and earthy mushrooms in a rich, garlicky cream sauce, topped with melty Gruyère (or Swiss) cheese and golden, crispy breadcrumbs. Baked until bubbling and beautifully browned, it delivers cozy comfort with fresh garden flavors in every forkful.

Why You’ll Love This Recipe

You’ll fall head over heels for this Baked Mushroom and Zucchini Gratin because it transforms simple, everyday vegetables into something truly special. The zucchini stays tender yet holds its shape, while the mushrooms bring deep, savory umami that pairs magically with the luxurious cream sauce infused with garlic and herbs.

Blanketed under a blanket of nutty, melty Gruyère (or your favorite cheese) and finished with buttery, golden breadcrumbs, every bite offers contrasting textures — creamy, crispy, soft, and earthy. It’s an elegant yet easy way to enjoy seasonal produce, feels restaurant-worthy without the fuss, works beautifully as a vegetarian main or crowd-pleasing side, and is surprisingly adaptable for different diets.

Whether you’re feeding family on a busy weeknight or impressing guests at a dinner party, this gratin delivers maximum flavor and satisfaction with minimal effort — pure cozy comfort food at its finest.

Yield: 6 servings

Baked Mushroom and Zucchini Gratin

Creamy, cheesy baked zucchini and mushrooms with golden breadcrumb topping — cozy, flavorful, and utterly irresistible.

Prep Time 20 minutes

Cook Time 40 minutes

Additional Time 10 minutes

Total Time 1 hour 10 minutes

Ingredients

4 medium zucchini (about 2 lbs / 900g), sliced into ¼-inch rounds
1 lb (450g) cremini or button mushrooms, sliced
1 medium onion, thinly sliced
3 cloves garlic, minced
1½ cups (360 ml) heavy cream
½ cup (120 ml) whole milk
1½ cups (150g) grated Gruyère cheese (or Swiss/Comté)
½ cup (50g) grated Parmesan cheese
¾ cup (75g) panko breadcrumbs
3 Tbsp butter, divided (2 Tbsp melted for topping)
2 Tbsp all-purpose flour
1½ tsp fresh thyme leaves (or ½ tsp dried)
½ tsp ground nutmeg (optional)
Salt and freshly ground black pepper, to taste
Olive oil, for sautéing

Instructions

Prep those gorgeous veggies — Wash the zucchini, trim the ends, and slice them into even ¼-inch rounds (a mandoline makes this super quick and uniform). Slice the mushrooms and onion thinly. Mince the garlic. This step sets you up for even cooking and beautiful layers — take your time here!
Draw out moisture — Place zucchini slices in a colander, sprinkle lightly with salt, and let them sit 15–20 minutes. This pulls out excess water so your gratin stays creamy instead of soupy. Pat them very dry with paper towels afterward — trust me, it’s worth it!
Sauté for maximum flavor — Heat 1 Tbsp olive oil and 1 Tbsp butter in a large skillet over medium-high heat. Add the sliced mushrooms and cook 6–8 minutes until golden and all liquid evaporates. Add onions and garlic; cook another 4–5 minutes until soft and fragrant. Season with salt, pepper, and half the thyme. Set aside — your kitchen already smells amazing!
Make the dreamy cream sauce — In the same skillet (or a saucepan), melt 1 Tbsp butter over medium heat. Stir in 2 Tbsp flour and cook 1 minute to make a roux. Slowly whisk in heavy cream and milk. Simmer gently 3–4 minutes until slightly thickened. Stir in nutmeg, remaining thyme, salt, and pepper. Remove from heat — this velvety base is what makes the gratin irresistible.
Preheat and prep the dish — Heat your oven to 375°F (190°C). Lightly grease a 9×13-inch (or similar) baking dish with butter or oil — this prevents sticking and adds extra richness.
Start layering the magic — Arrange half the zucchini slices in an even layer at the bottom. Scatter half the mushroom-onion mixture over top. Pour half the cream sauce evenly across everything, then sprinkle with half the Gruyère and a little Parmesan.
Repeat for beautiful layers — Add the remaining zucchini, mushrooms, and cream sauce. Finish with the rest of the cheeses — pile it on generously for that gooey, melty top we all crave!
Top it with crunch — Mix panko breadcrumbs with 2 Tbsp melted butter and a pinch of salt. Sprinkle evenly over the entire surface — this is the crown that turns golden and crispy in the oven.
Bake until bubbly and golden — Place in the center of the oven and bake 35–40 minutes, until the edges are bubbling and the top is deep golden brown. If you want extra crispiness, broil 1–2 minutes at the end (keep eyes on it!).
Rest and serve with love — Let the gratin rest 10 minutes before serving — this helps it set so slices hold together beautifully. Scoop generous portions onto plates and watch everyone go back for seconds!

Notes

This dish is naturally gluten-adaptable and can easily become vegetarian/vegan with simple swaps.
Leftovers reheat wonderfully in the oven — the topping stays crisp when warmed properly.
Pairs perfectly with grilled chicken, roasted meats, or a crisp green salad for a complete meal.

Nutrition Information

Yield

Serving Size

1
Amount Per Serving Calories 846Total Fat 58gSaturated Fat 34gUnsaturated Fat 24gCholesterol 175mgSodium 1135mgCarbohydrates 45gFiber 6gSugar 12gProtein 36g

The recipes and nutritional information on Yum Tonight are for informational purposes only. Always consult a healthcare provider for personalized dietary advice.

Recipe Tips and Tricks

Salt the zucchini slices lightly and let them sit 15–20 minutes to draw out excess moisture, then pat dry thoroughly — this prevents a watery gratin.
Sauté mushrooms and onions first to concentrate their flavor and avoid sogginess.
Use a mandoline for even, thin zucchini slices so everything cooks uniformly.
For extra-crisp topping, mix panko with melted butter and a touch of grated Parmesan before sprinkling.
Broil for the last 1–2 minutes if you love an ultra-golden, bubbly crust (watch closely to avoid burning).
Taste the cream sauce before assembling and adjust seasoning — mushrooms and zucchini love generous black pepper and a pinch of nutmeg.

Ingredients Notes

Zucchini forms the fresh, mild backbone — choose firm, medium-sized ones with bright skin for best texture and flavor. Mushrooms (cremini, button, or a mix with shiitake) deliver rich, meaty depth; never skip sautéing them first to evaporate liquid.

Heavy cream creates the silky base, while whole milk lightens it slightly without sacrificing richness. Gruyère brings nutty, melty perfection, but Swiss or a sharp cheddar works wonderfully too.

Garlic and thyme provide aromatic backbone — fresh thyme is especially fragrant. Panko breadcrumbs give the signature crisp topping; regular breadcrumbs are fine but panko stays lighter and crunchier. Butter adds richness to both sauce and topping. A touch of nutmeg (optional) enhances the creamy, cheesy elements beautifully without overpowering.

Variations and Substitutions

Make it gluten-free by swapping all-purpose flour for cornstarch or gluten-free flour and using GF panko breadcrumbs. For a lighter version, replace half the heavy cream with evaporated milk or use half-and-half.

Turn it vegan with plant-based cream, dairy-free cheese shreds, and olive oil instead of butter. Add protein by mixing in cooked shredded chicken, crispy bacon bits, or Italian sausage for a heartier main dish. Swap in yellow squash for half the zucchini for color contrast.

Experiment with cheeses — try fontina for ultra-creaminess, Parmesan for sharpness, or a mix with mozzarella for extra stretch. For more veggies, layer in sautéed spinach, leeks, or thin-sliced bell peppers. Spice lovers can add red pepper flakes or a dash of smoked paprika to the mushrooms.

Storage Options

Refrigerate leftovers in an airtight container for up to 3–4 days. Reheat in a 350°F (175°C) oven for 15–20 minutes until warmed through and topping re-crisps (cover loosely with foil if browning too fast). Microwave individual portions for 2–3 minutes, though the topping softens. Freezing is possible (up to 2 months) but texture may soften — thaw overnight in fridge and reheat in oven. Best enjoyed fresh, but still delicious the next day.