We heat the milk in the microwave on full power for a minute and a half. We whisk the heated milk into the roux slowly and increase to medium heat, stirring often until it comes to a boil.
Meanwhile, we heat the olive oil in a pan over medium heat and add the mushrooms. We saute until tender and the mushrooms have released their liquid. We add salt and pepper and keep on low heat until we are ready to serve.
When the pasta water comes to a boil, we add some salt, and the pasta, and cook until al dente.
Back to the milk pot, which we have been stirring often. When the mixture comes to a boil, we boil this on low heat for a few minutes. We add a little salt and pepper and a dash of nutmeg. We then remove it from the heat and add the gruyere and Locatelli.
When the pasta is done, we drain it in a colander. We combine the pasta and cheese sauce in the empty pot we used to boil the water. We stir to coat and spoon out two helpings for tonight’s meal. We top each serving with half the mushrooms and some red pepper flakes. The rest of the pasta we spoon into a 9×13 inch pan, cover with foil, and refrigerate for a baked macaroni and cheese tomorrow.