Ultimate Mac & Cheese: The Creamiest, Cheesiest Recipe

Preheat the oven to 350 degrees F (175 degrees C). Grease a 2-quart casserole dish.

Place bread crumbs into a small bowl and mix well with melted butter; set aside.

Bring a large pot of lightly salted water to a boil. Add macaroni and cook until al dente, 8 to 10 minutes; drain, then place into the prepared casserole dish.

While pasta is cooking, melt 2 tablespoons butter in a saucepan over medium heat. Stir in minced onion and cook until onion softens and turns translucent, about 5 minutes.

Stir in flour, salt, pepper, and dry mustard until incorporated, then pour in milk and bring to a simmer. Cook, stirring constantly, until milk has thickened, about 10 minutes.

Remove from heat and stir in Cheddar cheese until melted. Pour cheese sauce over macaroni, then sprinkle evenly with buttered bread crumbs.

Bake in the preheated oven until top is golden and bubbly, about 20 minutes.