Start by preheating your oven to 350°F (175°C) and greasing a 9x13-inch baking dish with butter or cooking spray. This ensures the casserole doesn’t stick and gets a crisp edge. If using fresh broccoli, lightly steam it for about 5 minutes until just tender. Frozen broccoli should be thawed and squeezed to remove any excess moisture to avoid a watery casserole.
In a large bowl, combine the cream of mushroom soup, freshly shredded cheddar cheese, mayonnaise, sour cream, garlic powder, onion powder, salt, and pepper. Stir everything until smooth and creamy. Add in the broccoli and gently fold it into the mixture, ensuring all florets are well coated. This will help infuse every bite with cheesy, savory flavor.
Spoon the broccoli mixture into your prepared baking dish and spread it evenly with a spatula. In a smaller bowl, combine the crushed butter crackers with melted butter and mix until the crumbs are fully coated. Sprinkle this mixture evenly across the top of the casserole. This crunchy topping adds irresistible texture and flavor.
Place the dish in the preheated oven and bake for 30–35 minutes. The casserole should be bubbling and the topping golden brown. Remove from the oven and let it rest for about 5 minutes before serving. This helps the casserole set up a bit, making it easier to serve clean portions.