Beat egg and cheese together until smooth. Add flour and salt. Turn out on a floured board, knead dough using no more than 1/2 cup flour. Roll into 3/4 inch diameter rope, cut each rope into 1/2 inch pieces. Push floured finger into center of each gnocchi. Drop gnocchi into boiling water. When they rise to the surface, cook 4 minutes. Drain and serve with favorite sauce, meatballs, sausage, etc.