Preheat oven to 350. Butter a shallow 1 1/2 quart baking dish, and add cooked macaroni.
In a blender or food processor combine egg, milk, and garlic, and process 3 seconds. Add onion, cheeses, peppers, salt, and paprika, and blend 10 seconds. Turn into dish, folding into macaroni. Casserole could be covered with plastic wrap and refrigerated up to 24 hours at this point.
To bake, bring casserole close to room temperature. Melt butter in a small saucepan. Coat crackers with butter and spread over top of casserole. Bake about 20 to 25 minutes, or until thick yet creamy. If top is not golden, slip under broiler for a minute. Remove from oven, let stand about 5 minutes, and serve.