1 lb. piccolini farfalle
3 tbsp. butter
1/2 onion, grated
3 tbsp. flour
2 cups milk
4 cups shredded Cabot cheddar cheese
½ tsp. mustard powder
1 tsp. salt
1 tsp. black pepper
Bring a large pot of water to a boil, add pasta and cook until al dente.
In another pot over low heat, melt butter, grate onion directly in and cook 5 minutes until softened. Season with salt and pepper. Sprinkle in flour and whisk to form a roux. Allow the flour to cook for a minute, then add in the milk. Bring to a soft boil, turn to low, whisk in the cheese slowly, a handful at a time. Stir in the mustard, taste and adjust seasonings.
Drain pasta very well, add to cheese sauce.
Mix to distribute. Pour into a baking dish, and bake at 400 for 30 minutes, until crisp on top.