Creating the Best French Onion Broccoli Cheese Casserole is simple if you follow these steps:

1. Preheat your oven to 350°F (175°C).
2. Prepare the Broccoli: In a pot of boiling water, blanch the broccoli florets for 3 minutes. Drain and set aside.
3. Cook the Onions: In a skillet over medium heat, add olive oil and sauté the sliced onions until they are caramelized, about 10-12 minutes. Stir occasionally to prevent burning.
4. Mix Ingredients: In a large mixing bowl, combine the sour cream, cheddar cheese, mozzarella cheese, French onion soup, garlic powder, salt, and black pepper. Mix until well combined.
5. Add Broccoli and Onions: Gently fold in the blanched broccoli and caramelized onions until evenly distributed throughout the mixture.
6. Transfer to Baking Dish: Pour the mixture into a greased 9×13-inch baking dish, spreading it evenly.
7. Prepare the Topping: In a separate bowl, mix the breadcrumbs and grated Parmesan cheese. Sprinkle this mixture evenly over the casserole.
8. Bake: Place the casserole in the preheated oven and bake for 30-35 minutes, or until the top is golden brown and the casserole is bubbling.
9. Cool Slightly: After baking, allow the casserole to cool for about 5 minutes before serving. This will help set the layers and enhance the flavors.

These straightforward steps will guide you in creating this incredible casserole effortlessly.