Cheesy Spinach Casserole – A Creamy, Comforting Delight

2 tablespoons butter (or olive oil)
1 small onion, finely chopped
3 garlic cloves, minced
2 (10-ounce) packs frozen spinach, thawed and well-drained (or 6 cups fresh spinach, sautéed)
1 cup ricotta cheese (or cottage cheese for a lighter version)
½ cup sour cream (or Greek yogurt for a tangy twist)
½ teaspoon salt
½ teaspoon black pepper
½ teaspoon ground nutmeg (optional, enhances flavor)
1 teaspoon Italian seasoning
1 cup shredded cheddar cheese (or a mix of mozzarella and Parmesan)
½ cup grated Parmesan cheese
½ cup breadcrumbs (for a crispy topping, optional)
2 eggs, lightly beaten (for binding)