The ham is cut into thin slices. The cheese sauce is prepared by melting butter, adding flour and frying while stirring. Gradually add milk, and if necessary, use more than 6 1/5 cups (1.5 liters), so the sauce does not become too thick. Add the grated cheese and cheese sauce, boil it until it is melted.
Grease a large fire-proof oven dish and begin to stack the lasagna, alternating between sheets, cheese sauce and ham in layers. Finish off with a sheet and pour in the remaining sauce. Sprinkle it with plenty of grated cheese and put it to bake in a preheated oven at 392°F (200 °C) for 30 minutes.