This recipe makes two jelly roll pans of bars, which are frosted and put together. Refrigerate half of the batter while you're baking the first pan.

1. Preheat oven to 350°F.

2. Line two 10″ × 15″ jelly roll pans with foil; grease foil and set aside.

3. In large bowl, combine cake mix, pudding mix, eggs, and 1½ cups milk. Beat until combined, then beat at medium speed for 2 minutes.

4. Divide into prepared pans. Bake for 15–20 minutes or until set.

5. Let cool in pans for 30 minutes, then invert onto kitchen towels sprinkled with powdered sugar. Let cool completely.

6. In saucepan, combine flour, cocoa powder, and ½ cup milk; mix with wire whisk.

7. Cook over medium heat until thick, then stir in vanilla and chill until cold.

8. In bowl, beat together sugar and margarine until sugar dissolves. Gradually beat in the chilled flour mixture until very fluffy.

9. Spread on one bar, top with the second.

10. Let stand until set, then slice bars and wrap in plastic wrap.