Cook the macaroni according to the package directions.
Preheat the oven to 350 F.
To make the cheese sauce, melt the butter in a large saucepan and cook the onion in the butter until the onion is translucent.
Stir in the flour, salt, and pepper.
Add the milk to the pan and stir until the mixture is thick and bubbly.
Cook for 1-2 minutes more before adding the cheese. Continue stirring until the cheese is completely melted.
Add the cooked macaroni to the sauce and stir until combined.
Add the mixture to a casserole dish.
Crumble the topping over the macaroni and cheese mixture.
Cook in the oven for 30-35 minutes.
Extra: Add ketchup to the top and ENJOY!