�Saute the onion, green onion, celery and carrot in the butter until tender. Add the salt, pepper, ground beef and a few spoons of water. Saute a few minutes and add the tomatoes. Leave the meat with the sauce to simmer for half an hour. Remove from the heat and add the lightly beaten egg whites. Boil 4 kilos water with a tablespoon salt. Put in the macaroni and leave it to boil for 10 minutes. Add one cup cold water and then drain the macaroni. While macaroni is cooking, prepare the Bechamel Sauce: Put the 3 tablespoons butter and the flour into a saucepan. Stir over slow fire until smooth. Add the milk, gradually, whisking with a wire whisk or electric mixer. Continue cooking until sauce thickens. Remove from the fire and add salt and pepper to taste (optionally, grated nutmeg is also good). Lightly beat the egg yolks, then add a few spoonfuls of the hot sauce to them, and mix well. Then add the egg yolks to the the rest of the Bechamel sauce, mixing them in well. Set aside. Put the unsalted butter into the macaroni and then put half the macaroni into a rectangular baking pan. Sprinkle with plenty of grated cheese and then cover with the meat. Put the remaining macaroni on top and cover with cheese. Pour the Bechamel Sauce over. Bake for about 40 minutes in a medium oven. Cut into squares when slighly cooled and serve.