To each egg 1/2 its weight in grated cheese and a 1/2 ounce of butter (if only 1 egg is prepared 1/2 ounce of butter must be used); mustard, pepper, and salt to taste. Whip up the eggs, add 1 dessertspoonful of water for each egg; mix in the cheese, a little made mustard, and pepper and salt. Heat the butter in a frying-pan or small stewpan. When hot stir in the mixture of egg and cheese. Keep stirring it with a knife, until it becomes a smooth and thickish mass. Put on hot buttered toast, and serve. This is an extremely tasty French dish. The mixture, when cold, is excellent for sandwiches.