In a medium pot boil the milk on low heat. Keep aside.

In a medium non-stick pot over medium heat add the butter and whisk. Once melted and frothed start adding the flour and keep on whisking to be just enough thick, a nice roux and the flour smell has gone.

At this point start adding the warm milk, a bit at a time and keep on whisking. Continue adding the milk and keep on whisking aiming to achieve a nice, not too runny cream.

Reduce the heat to low and cook while stirring frequently, until sauce is thick enough to coat back of a wooden spoon, about 3 minutes. Add slowly the cheeses, if you add them altogether there is a chance of curdling, and whisk until smooth, moving saucepan on and off heat to keep it hot enough to melt the cheese but not so hot that it bubbles rapidly. Season with salt and pepper and set aside.