This recipe is from my grandmother. She used to prepare it on special occasions, and all the family gathered to enjoy it. Despite it has an small amount of liquor (rum), it's ok for kids, and you will find them asking for another slice!
Preheat oven to 350 degrees F.
Beat egg yolks and 1/4 cup sugar until thick and smooth. Stir in flour, cocoa and vanilla extract. Blend well. Whip egg whites until stiff, but not dry. Fold into yolk and flour mixture.
Butter a 15 x 8-inch baking pan. Line with baking parchment paper or wax paper. Butter well again, and dust lightly with 2 tablespoons of the confectioners' sugar.
Pour batter into the pan and spread out evenly. Bake for 15 minutes. Cool for 5 minutes, then turn onto a cloth to cool. After 10 minutes peel paper off.
Combine whipped cream, rum and sugar. Adjust to taste. Spread over cake and roll cake like a jellyroll, starting with the long edge. Sprinkle with remaining confectioners' sugar. Serve in slices.