Spray a heavy, medium-sized shallow rectangular pan with cooking spray. Line the pan with waxed paper, and also spray paper.
In a medium mixing bowl, beat egg whites and cream of tartar on medium speed until foamy. Add 1/4 cup sugar and beat on high speed until soft peaks form. Set aside.
In a separate medium mixing bowl, beat oil and 1/2 cup sugar on medium speed. Add the vanilla and then the sifted flour, and mix until well blended. Fold 1/4 of the egg whites into the batter. Then carefully fold in the remaining egg whites. Spread the batter evenly into the pan.
Bake for 12 minutes, or until lightly browned. The cake should spring back when touched lightly. While cake is still warm, loosen it from the pan, and sprinkle it with some of the powdered sugar. Cover cake with a baking cloth. Invert the cake by placing a large cookie sheet over the cloth and turning the cake over. Remove the waxed paper and roll the cake in the cloth. Cool the cake on a wire rack while mixing the filling. Do not let cake cool longer than it takes to mix the filling or it will become too stiff to handle.
For the filling, mix the cream cheese, sour cream, jam, and strawberries together in a medium bowl until well blended.
Unroll the cake. Spread the filling on the cake, leaving a 1/2-inch border. Carefully re-roll the cake.
Garnish with powdered sugar.
A viewer or guest of the show, who may not be a professional cook, provided this recipe. It has not been tested for home use.