Beat egg until light, add sugar gradually, milk, flour mixed and sifted with baking powder and salt, then butter. Line the bottom of a dripping-pan with paper; butter paper and sides of pan. Cover bottom of pan with mixture, and spread evenly. Bake twelve minutes in a moderate oven. Take from oven and turn on a paper sprinkled with powdered sugar. Quickly remove paper, and cut off a thin strip from sides and ends of cake. Spread with jelly or jam which has been beaten to consistency to spread easily, and roll. After cake has been rolled, roll paper around cake that it may better keep in shape. The work must be done quickly, or cake will crack in rolling.