Grease a baking tray with butter. Cover the tray with aluminum foil and grease it as well (very, very important!). Sprinkle the tray with breadcrumbs.
Put the butter in a saucepan and let it melt. Once melted, add the flour and stir for 2 minutes to cook it. Then add the warm milk in 3 parts, whisking continuously. Let it boil and then lower the heat until it thickens slightly. Remove from heat and let cool.
Add the grated cheese and the yolks to the (cooled) white sauce and stir.
Beat the egg whites along with the cream of tartar and salt until stiff peaks form.
Gently fold the beaten egg whites into the white sauce. Spread it over the tray with a spatula to cover the entire surface.
Bake for 15 minutes, remove from the oven (it should not brown), let it cool a bit, and roll it with the aluminum foil. Put it in the refrigerator.
Once the filling is ready (tomato sauce with mushrooms, strips, ham, and cheese, or whatever you have in mind), heat the filling and fill the roll. Bake it in the oven for a few minutes.
Serve hot in slices.
Nutritional Information
* * Information per 100g serving, percentage of daily values based on a 2,000 calorie diet.
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