1 box Betty Crocker® SuperMoist® white cake mix
Water, vegetable oil and egg whites called for on cake mix box
3/4 cup miniature semisweet chocolate chips
1/4 cup chocolate-flavor syrup
1 container Betty Crocker® Rich & Creamy vanilla frosting
Additional chocolate-flavor syrup, if desired

1. Heat oven to 350°F (325°F for dark or nonstick pan). Generously grease, or spray with baking spray with flour, bottom of 13×9-inch pan.
2. Make cake batter as directed on box–except stir in 1/2 cup of the chocolate chips. Reserve 1 cup of the batter. Pour remaining batter into pan. Stir 1/4 cup chocolate syrup into reserved batter. Drop by generous tablespoonfuls randomly in 6 to 8 mounds onto batter in pan. Cut through batters with spatula or knife in S-shaped curves in one continuous motion. Turn pan 1/4 turn, and repeat cutting for swirled design.
3. Bake 33 to 37 minutes (36 to 40 minutes for dark or nonstick pan) or until toothpick inserted in center of chocolate comes out clean. Run knife around sides of pan to loosen cake. Cool completely, about 1 hour. Stir remaining 1/4 cup chocolate chips into frosting. Spread frosting over top of cake; drizzle with additional chocolate syrup. Store loosely covered at room temperature.