Preheat oven to 350°F; grease a 9x13-inch dish with spray or butter.
Steam or blanch broccoli in boiling water 3-4 minutes until bright green and slightly tender; drain very well and pat dry.
Mix soup, sour cream, mayonnaise, milk, 2 cups cheddar, garlic powder, onion powder, salt, and pepper in large bowl until smooth.
Gently fold in broccoli to coat; spread evenly in dish.
Combine crackers, butter, and remaining 1/2 cup cheese in small bowl; sprinkle evenly over broccoli.
Bake uncovered 30-35 minutes until edges bubble and topping is golden brown.
Stand 5 minutes to set slightly before serving.