While pasta is cooking, heat milk in a small saucepan over
medium heató do not let simmer.
In a medium saucepan, make a roux with the butter and the
flour. Stir 1 to 2 minutes , until golden.
Slowly whisk in warm milk. Add nutmeg, salt and pepper.
Cook sauce, whisking often, until thickenedó about 10
minutes. Remove from heat.
Add heavy cream and half of the gruyere cheese. Stir until
cheese is melted.