Put the milk on, and when it boils add salt. Take a wooden spoon and, stirring constantly, add the farina little by little. Cook for ten minutes, stirring constantly. Take off the fire and break into the farina one egg; mix very quickly, so that the egg will not have time to set. Spread the farina onto the breadboard about the height of a finger. Allow it to cool, then cut it into squares or diamonds about two or three inches across. Butter well a baking-dish, and put in the bottom a layer of the squares of farina; sprinkle over a little grated Parmesan cheese (or Gruyere), and put here and there a small dab of butter. Then put in another layer of the squares of farina; add cheese and butter as before. Continue in this way until your baking-dish is full, having on the top layer butter and cheese. Bake in a hot oven until a brown crust forms. Serve in the baking-dish.