The first step is to cook the macaroni in a pot with enough water and salt. When al dente and drain them out. Now in a good size pot will take a little oil and a little butter. Chop the onion and sauté in the pan, then add a tablespoon of flour and slowly pouring the hot milk going while we are removing. If we see that is too thick you can add some leftover broth when baked macaroni
When this sauce is to our liking we add cooked macaroni, put it in a baking dish and sprinkle grated cheese over abundant
Only is put in the oven and leave the time required for gratinen.