Go Back Email Link
Print Pin

Cheesy Vegetable Gratin (Mornay-Style)

A rich, layered vegetable gratin made with a creamy cheese sauce and a lightly set custard base. Perfect for using a mix of sturdy and tender vegetables while keeping a sliceable, not watery, texture.
Course Brunch, Side Dish
Cuisine American, French-inspired
Prep Time 25 minutes
Cook Time 34 minutes
Total Time 1 hour
Servings 8
Author sunny

Equipment

  • large baking dish (9" x 13")
  • sheet pan
  • saucepan
  • cheese grater
  • whisk

Ingredients

vegetables

  • 2 cups carrots, thickly sliced
  • 1 1/2 cups celery, sliced diagonally
  • 1 1/2 cups thin green beans, trimmed (whole or halved)
  • 1 1/2 cups zucchini, cut into thick half-moons
  • 1 1/2 cups yellow summer squash, cut into thick half-moons
  • 1 1/2 cups sweet onion, sliced into thick half-moons

cheese sauce

  • 4 tbsp. butter
  • 1/4 cup all-purpose flour
  • 2 cups whole milk
  • 1 cup cheddar cheese, grated
  • 1 cup Swiss cheese, grated
  • 1 tsp. kosher salt
  • 1/2 tsp. black pepper
  • 1/2 tsp. nutmeg

custard

  • 2 eggs

topping

  • 1/2 cup white cheddar cheese, grated
  • 1/2 cup Swiss cheese, grated

Instructions

prepare the vegetables

  • Preheat the oven to 425°F. Toss all vegetables lightly with oil and salt, then spread on a sheet pan in an even layer. Roast for 15-20 minutes, just until the vegetables begin to soften and release moisture. Remove and set aside.
  • Reduce oven temperature to 350°F.

make the cheese sauce

  • In a saucepan over medium heat, melt the butter. Whisk in the flour and cook for 2-3 minutes, until lightly golden and no longer raw-smelling.
  • Gradually whisk in the milk, cooking until the sauce thickens enough to coat the back of a spoon.
  • Stir in cheddar, Swiss, salt, pepper, and nutmeg until smooth.

add the eggs

  • In a separate bowl, lightly beat the eggs. Slowly whisk in a small amount of the hot sauce to temper the eggs, then return the mixture to the saucepan. Stir gently to combine. Do not boil.

assemble the gratin

  • Lightly grease a 9" x 13" baking dish. Layer the vegetables evenly, adding some sauce between layers. Pour remaining sauce over the top, ensuring it fills the gaps.
  • Sprinkle the remaining cheddar and Swiss cheese evenly over the top.

bake

  • Bake at 350°F for 30-40 minutes, until bubbling around the edges, set in the center, and golden on top.
  • Let rest for 10 minutes before serving.

Notes

  • Cut vegetables into large, even pieces.
  • Pre-cooking the vegetables is essential to prevent excess moisture in the final dish.
  • For extra flavor, add a teaspoon of Dijon mustard or a splash of lemon juice or vinegar to the sauce.
  • For a crisp topping, add a light layer of breadcrumbs before baking.