Heat oven to 375°F. Line bottom only of 15x10x1-inch pan with waxed paper; spray with baking spray and sprinkle with flour. (For the extra batter, place paper baking cups in 8 regular-size muffin cups.)

In large bowl, beat eggs with electric mixer on high speed about 5 minutes or until thick and lemon colored. Add cake mix, water and oil; beat on low speed 30 seconds, then on medium speed 1 minute, scraping bowl occasionally. Pour 3 1/2 cups batter into pan. Divide remaining batter among muffin cups.

Bake 14 to 16 minutes or until cake springs back when lightly touched in center and cupcakes test done when toothpick inserted in center comes out clean. If necessary, run knife around edges of pan to loosen cake. Turn cake upside down onto clean kitchen towel sprinkled with 1 tablespoon powdered sugar; carefully remove pan liner. While hot, carefully roll up cake and towel from narrow end. 

Cool rolled cake completely on cooling rack, about 1 hour.  [Cool cupcakes and save for another use.]

When cool, unroll the cake carefully, and remove towel. Spread vanilla frosting evenly over inside of cake. Carefully roll up cake without the towel. Place cake roll on serving plate. Frost the outside of cake with chocolate frosting. Using fork, drag tines through frosting to look like log. 

Store loosely covered in refrigerator. Let stand at room temperature 30 minutes before serving.