Preheat oven to 400° F.
In a skillet, melt butter. Add flour and mix. When it gives off the scent of hazelnut, start adding the milk, stirring. When the sauce is made, add the Ile de France Roquefort, diced. Stir to melt. Add the drained mushrooms.
Alternating a layer of lasagne sheets, 2 slices of smoked ham, and a ladle or two of sauce. End with layer of lasagna sheets and remaining sauce. Cover with grated cheese and bake 30 minutes.