Description
Hearty French onion soup casserole merges classic bistro flavors with comforting casserole textures. Caramelized onions, crusty bread, and melted Gruyère cheese create a satisfying dish you’ll savor down to the last golden-brown bite.
Ingredients
Scale
- 5 Vidalia onions (medium, thinly sliced, about 1.36 kg or 3 lbs)
- 16 oz (454 g) baguette, thinly sliced
- 8 oz (226 g) Gruyère cheese, shredded (about 2 cups)
- 3 cups reduced-sodium beef broth
- ¼ cup unsalted butter
- ⅓ cup all-purpose flour
- ½ cup sherry
- 2 tsps kosher salt
- ½ tsp black pepper
- 3 thyme sprigs
- 2 flat-leaf parsley sprigs
- 2 bay leaves
- 1 tsp fresh thyme leaves
Instructions
- Caramelization: Heat butter in a Dutch oven over medium-low temperature. Combine whole onions, kosher salt, black pepper, dried thyme, parsley sprigs, and bay leaves, slowly cooking for 60 minutes until onions transform into a rich, golden-brown color with deep, sweet flavor.
- Bread Preparation: Preheat oven to 350°F. Slice baguette into thin, uniform pieces and arrange on a baking sheet. Toast for 12-15 minutes until crisp and light golden.
- Roux Development: Remove herb sprigs and bay leaves from caramelized onions. Dust with all-purpose flour, cooking for 2 minutes while stirring to create a smooth base. Pour in beef broth and dry sherry, bringing to a rolling boil and cooking 2-3 minutes until sauce thickens and becomes glossy.
- Layering: In a 13 x 9-inch baking dish, create a foundation using half the toasted baguette slices. Spoon onion mixture evenly over bread, then top with remaining baguette pieces.
- Cheese Topping: Generously sprinkle grated Gruyère or Swiss cheese to completely cover the surface.
- Baking Process: Cover with aluminum foil and bake for 25-30 minutes. Remove foil, switch oven to broil, and cook 2-3 minutes until cheese bubbles and develops a golden-brown crust.
- Serving: Garnish with freshly chopped thyme leaves and serve immediately while hot and aromatic.
Notes
- Maximize Onion Sweetness: Slow cooking at low heat for 60 minutes develops a deep, caramelized flavor that transforms ordinary onions into a rich, sweet base.
- Perfect Bread Texture: Toast baguette slices separately to ensure crispy, golden edges that maintain structure when layered in the casserole.
- Roux Technique: Stirring flour continuously prevents lumps and creates a smooth, glossy sauce that binds the onion mixture perfectly.
- Cheese Melting Hack: Broiling uncovered for 2-3 minutes creates a golden, bubbly cheese crust that adds incredible texture and visual appeal.
- Prep Time: 1 hour 20 minutes
- Cook Time: 45 minutes
- Category: Dinner, Appetizer
- Method: Baking
- Cuisine: French
Nutrition
- Serving Size: 7
- Calories: 350
- Sugar: 6 g
- Sodium: 500 mg
- Fat: 15 g
- Saturated Fat: 9 g
- Unsaturated Fat: 4 g
- Trans Fat: 0 g
- Carbohydrates: 43 g
- Fiber: 3 g
- Protein: 10 g
- Cholesterol: 35 mg