Brush jelly-roll pan, 10” x 15”, with oil, line it with wax paper, and oil the paper.
Separate eggs.
Using heavy whisk, beat the yolks with sugar until the mixture is pale in color and thick enough to “ribbon”. Beat in ground walnuts and baking powder. Fold in egg whites, stiffly beaten.
Spread the batter in the prepared pan and bake the cake in a moderate oven (350° F) for 15 to 20 minutes, or until it is golden.
Cool the cake in the pan, cover it with a damp towel, and chill it.
Dust the cold cake generously with sifted confectioners sugar and turn it out on a board covered with two overlapping sheets of waxed paper.
Carefully strip the paper from the bottom of the cake.
Spread the cake with heavy cream, whipped and flavored with sugar and vanilla to taste.
Roll up the cakes, using the paper as an aid, and slide the roll onto a flat serving platter.
Sprinkle the roll with more sifted confectioners sugar.