Preheat oven to 350°

1. Melt the butter in a medium saucepan over medium-low heat.

2. Slowly whisk in the flour. Continue cooking it until the nutty flour scent dissipates.

3. Add the evaporated milk in a thin, steady stream, whisking constantly to prevent lumps. Continue to cook, whisking, until the sauce thickens.

4. Add the salt, pepper, 2 ½ cups of cheese, the ketchup, and mustard. Taste and correct the seasoning according to your preference.

NOTE: If the sauce is lumpy, pour it into a blender and blitz until smooth.

5. Place 2 cups of cooked elbow macaroni into a greased oven-proof baking dish.

6. Pour in the cheese sauce and mix completely.

7. Let the macaroni and cheese sit for 15 minutes to allow the macaroni to absorb the sauce.

8. Sprinkle the remaining ½ cup of cheese on top and bake in the preheated oven for 20 to 25, or until the sauce bubbles in the center.