Preheat the oven: Preheat your oven to 350°F (175°C) and grease a 9×9-inch casserole dish.
- Blanch the broccoli: Boil the broccoli for 2-3 minutes, then drain and set aside to cool.
- Make the casserole filling: In a large bowl, combine mayonnaise, sour cream, cream of mushroom soup, 1 cup of shredded cheddar cheese, garlic powder, onion powder, salt, and pepper. Mix until smooth.
- Assemble the casserole: Add the cooked broccoli to the creamy mixture and stir to coat. Transfer the mixture to the casserole dish and spread evenly.
- Prepare the topping: Mix the crushed crackers or breadcrumbs with melted butter, then sprinkle over the casserole.
- Bake: Bake for 25-30 minutes until the top is golden brown and the casserole is bubbling around the edges.
- Serve: Let the casserole cool for a few minutes before serving. Serve warm as a side dish or light main course.