Croissant and Salmon Breakfast Casserole

Name: Croissant and Salmon Breakfast Casserole
Prep time: 20 min
Cook time: 55 min
Total time: 1 h 15 min
Cuisine: American
Ingredients: 3 tablespoons butter; ½ white onion, chopped; 2 cloves garlic, minced; 12 eggs; ½ cup milk; 6 croissants, split - tops set aside and bottoms torn into 1-inch pieces; 2 green onions, thinly sliced; 4 ounces smoked salmon, chopped; 1 cup shredded Monterey Jack cheese; 1 cup shredded Swiss cheese; 1 cup shredded mozzarella cheese; 2 tablespoons chopped fresh dill; 1 teaspoon salt; freshly cracked black pepper to taste