Preheat oven to 350 degrees F (175 degrees C). Grease an 8-inch square baking dish.
Place bacon in a large skillet and cook over medium heat until just slightly cooked, about 5 minutes. Drain the bacon slices on paper towels and cut into pieces.
Mix 3/4 cup crushed crackers, corn, broccoli, onion, egg, and butter in a bowl; spoon mixture into the prepared baking dish. Sprinkle with 1/4 cup crushed crackers; top with bacon. Cover dish with aluminum foil.
Bake in the preheated oven for 30 minutes. Remove cover and continue baking until bacon is crisp and casserole is cooked through, about 30 more minutes.