This Layered Vegetable Gratin is a colorful and elegant side dish made with thinly sliced potatoes, zucchini, yellow squash, tomatoes, and onions layered in a creamy garlic herb sauce and topped with melted cheese. Baked until tender and golden, it’s a delicious addition to holiday dinners or a healthy weeknight meal.

Recipe Overview

Ingredients

Vegetables

• 2 medium Yukon Gold potatoes, thinly sliced
• 2 medium zucchini, thinly sliced
• 2 medium yellow squash, thinly sliced
• 2 large Roma tomatoes, thinly sliced
• 1 medium onion, thinly sliced

Garlic Cream Sauce

• 2 tablespoons unsalted butter
• 2 cloves garlic, minced
• 2 tablespoons all-purpose flour
• 1½ cups whole milk
• ½ cup heavy cream
• ½ teaspoon salt
• ½ teaspoon black pepper
• ½ teaspoon Italian seasoning
• ¼ teaspoon ground nutmeg (optional)

Cheese Topping

• 1 cup shredded Gruyère cheese
• ½ cup shredded mozzarella cheese
• ¼ cup grated Parmesan cheese

Garnish

• 2 tablespoons chopped fresh parsley
• Fresh thyme leaves (optional)

Equipment Needed

• 9-inch round or 9×13-inch baking dish
• Mandoline slicer or sharp knife
• Medium saucepan
• Whisk
• Aluminum foil

Instructions

Step 1: Preheat the Oven

Preheat the oven to 375°F (190°C).

Lightly grease the baking dish with butter or cooking spray.

Step 2: Prepare the Sauce

Melt the butter in a saucepan over medium heat.

Add the garlic and cook for 30 seconds.

Whisk in the flour and cook for 1 minute.

Slowly whisk in the milk and heavy cream.

Season with:

• Salt
• Black pepper
• Italian seasoning
• Nutmeg (if using)

Cook for 4–5 minutes, stirring frequently, until slightly thickened.

Step 3: Layer the Vegetables

Arrange the sliced vegetables vertically or in overlapping rows, alternating:

• Potato
• Zucchini
• Yellow squash
• Tomato
• Onion

Continue until the dish is full.

Step 4: Add the Sauce

Pour the garlic cream sauce evenly over the vegetables.

Gently shake the baking dish so the sauce settles between the layers.

Step 5: Add the Cheese

Sprinkle evenly with:

• Gruyère
• Mozzarella
• Parmesan

Step 6: Bake

Cover loosely with aluminum foil.

Bake for 40 minutes.

Remove the foil and continue baking for 20 minutes, or until:

• The vegetables are tender.
• The cheese is bubbly.
• The top is golden brown.

For extra browning, broil for 2–3 minutes at the end.

Step 7: Serve

Allow the gratin to rest for 10 minutes.

Garnish with fresh parsley and thyme before serving.

Tips for the Best Vegetable Gratin

Slice Evenly

Use a mandoline slicer for uniformly thin slices so everything cooks at the same rate.

Pat Tomatoes Dry

Blot tomato slices with paper towels to reduce excess moisture.

Use Freshly Grated Cheese

Freshly grated cheese melts more smoothly and creates a better crust.

Let It Rest

Resting allows the creamy sauce to set, making the gratin easier to serve.

Flavor Variations

Mediterranean

Add sliced eggplant, roasted red peppers, crumbled feta, and olives.

Bacon Lovers

Sprinkle cooked, crumbled bacon between the vegetable layers.

Herb Garden

Add fresh rosemary, basil, thyme, and oregano.

Spicy

Mix crushed red pepper flakes into the cream sauce.

Low-Carb

Replace the potatoes with extra zucchini and eggplant.

What to Serve With

Main Dishes

• Roast chicken
• Grilled steak
• Baked salmon
• Pork tenderloin
• Roast turkey

Salads

• Caesar salad
• Greek salad
• Mixed greens with balsamic vinaigrette

Bread

• Garlic bread
• French baguette
• Dinner rolls

Storage Instructions

Refrigerator

Store leftovers in an airtight container for up to 4 days.

Freezer

Freeze after baking for up to 2 months.

Thaw overnight in the refrigerator before reheating.

Reheating

Oven

Bake at 350°F (175°C) for 15–20 minutes until heated through.

Microwave

Heat individual servings for 1–2 minutes.

Nutrition Information (Per Serving)

Frequently Asked Questions

Can I prepare this ahead of time?

Yes. Assemble the gratin up to 24 hours in advance, cover, and refrigerate. Bake just before serving.

Can I make it vegetarian?

Yes. This recipe is already vegetarian. Just ensure the cheeses used are made with vegetarian rennet if needed.

Can I use different vegetables?

Absolutely. Eggplant, sweet potatoes, mushrooms, or bell peppers are all excellent additions.

Why is my gratin watery?

Vegetables like tomatoes and zucchini release moisture as they cook. Pat them dry before layering, and let the gratin rest after baking so the sauce thickens.

Can I make it gluten-free?

Yes. Replace the all-purpose flour with a gluten-free flour blend or use 1 tablespoon of cornstarch to thicken the sauce.

Recipe Notes

✅ Vegetarian

✅ Family-friendly

✅ Perfect for holidays or dinner parties

✅ Great make-ahead side dish

✅ Rich, creamy, and colorful

Make-Ahead Tip

Slice the vegetables and prepare the cream sauce up to one day in advance. Store them separately in the refrigerator, then assemble and bake when ready to serve.

Serving Suggestion

Pair this gratin with grilled chicken, roasted beef, baked salmon, or a crisp green salad. It’s also delicious as a light vegetarian main course with crusty bread.

Chef’s Secret

For a beautifully layered presentation, arrange the vegetables in tightly packed overlapping rows. Finish the gratin under the broiler for 2–3 minutes to achieve a deeply golden, bubbly cheese crust, and garnish with fresh herbs just before serving for a burst of color and flavor.