In a large pot, bring salted water to boil and cook your noodles.

Drain noodles and set aside.

Using the same pot (or a new one if you like to do dishes), melt the butter over medium high heat until bubbly. Whisk in the flour, one tablespoon at a time, making sure to fully cook each addition.

Cook the flour until it is no longer raw. The mixture (a roux) should be thick and pale yellow.

Add in the milk, while whisking. Continue cooking until the mixture thickens and is creamy.

Season with salt, pepper and red pepper flakes. Remove from heat and stir in your cheese(s). Stir until fully melted and incorporated.

Add your drained pasta to the cheese mixture and stir to fully coat.