In this recipe a roux is used to produce a creamy béchamel sauce. Roux is made from equal parts flour and butter, cooked together and used to thicken sauces.

To prepare sauce: Heat the milk in a medium saucepan over medium heat. When milk comes just to a simmer, reduce heat to low, careful not to let the milk boil up and spill over the sides.

To a large saucepan over medium-high heat, add the butter. When the foaming subsides, add the onion and garlic; cook until soft and translucent, about 4 minutes. Whisk in the flour and keep whisking until the roux turns a pale blonde color and is bubbling. Gradually ladle the warm milk into the roux. Whisking constantly, bring the mixture to a boil. Reduce heat to a simmer and cook until sauce has thickened, 5 minutes. Add half of the cheese, salt and pepper; stir until cheese has melted and the sauce is smooth.

To cook pasta: Heat a large pot of water over high heat until boiling. Generously season water with salt. Add pasta to the water and stir to prevent noodles from sticking together. Boil until al dente, about 10 minutes. Reserve about one cup of pasta water and drain pasta through a colander.

Transfer pasta to the saucepan with the cheese sauce and add the remaining grated cheese; mix well, adding the reserved pasta water to loosen sauce as needed. Taste and adjust seasoning with salt and pepper.

To serve: Divide pasta among warm pasta bowls and serve immediately.