French Onion Casserole

Square front shot of French onion casserole in a white baking dish.

Print Pin

5 from 5 votes

A must-serve side dish or easy meatless dinner for all of your cozy gatherings this season!

Course Dinner, Main Course, Side Dish

Cuisine American

Keyword french onion casserole, French Onion Soup Casserole, Onion Casserole

Prep Time 10

Cook Time 1 30

Total Time 1 40

Servings servings

Calories 238kcal

Author Blair Lonergan

Ingredients

3 medium sweet onions, sliced
3 tablespoons salted butter
4 cups beef broth (use vegetable broth or vegetable stock for a vegetarian dish)
1 teaspoon Worcestershire sauce
4 ounces French baguette bread, sliced about ½-inch in thickness (approximately 10-12 small slices)
1 cup (4 ounces) shredded mozzarella cheese (or sub with Gruyere or Fontina when available)
¼ cup grated Parmesan cheese
Optional garnish: chopped fresh thyme or parsley

Instructions

Preheat the oven to 350°F. Grease a medium casserole dish (approximately 2 quarts, or about 11 x 7-inches or 9-inches square). Set aside.
Melt the butter in a large saucepan over low heat.
Add the onions and cover. Cook for about 30 minutes, stirring occasionally.
Add the beef broth and the Worcestershire sauce; bring to a boil.
Reduce the heat to low. Allow the liquid to simmer, uncovered, for about 30 minutes so that the broth reduces.
Pour the onion and broth mixture into the prepared baking dish.
Lightly toast the slices of bread.
Arrange the toasted bread in a single layer on top of onion and broth mixture.
Cover the bread with a thick layer of shredded mozzarella. Sprinkle grated Parmesan over top.
Bake, uncovered, for 20-30 minutes, or until cheese is melted and lightly browned on top. If you prefer a darker, crispier topping, you can place the dish under the broiler for the final 1-2 minutes (just keep a close eye on it so that it doesn't burn). Garnish with chopped fresh herbs, if desired.

Notes

Want to Prep Ahead? Prepare the French onion soup base for the casserole (through Step 6) up to a day or two in advance. Keep it covered in the refrigerator until you're ready to bake it. Before baking, allow the dish to sit on the counter for at least 30-60 minutes so that it has time to come to room temp before you assemble and bake the casserole.

I also like to toast the bread in advance. Allow the toast to cool completely and then just store it in a zip-top bag on the counter until you're ready to bake the casserole.

Leftovers will keep in an airtight container in the fridge for 3-4 days; however, the bread will get soggy as it sits.

Nutrition