Peel the potatoes. Grate them coarsely, and add a little salt. Squeeze lightly to get rid of excess juice.Mix together with the egg, salt and pepper, and form small fritters. In a large frying pan, heat the oil or butter and spoon in 4 fritters. Press flat. Fry golden brown on both sides and set aside on a kitchen paper. Keep warm in the oven at 70 °C. Heat butter in a pan. Carefully fry the four eggs. Brush the truffles well with a vegetable brush and cut into fine slices. Place one fritter each on a warmed plate, and put a fried egg on top of each fritter. Serve with sliced truffles as decoration.