1Heat oven to 350°F. Grease 13x9-inch pan with shortening. In large bowl, beat all cake ingredients with electric mixer on low speed 30 seconds, scraping bowl often. Beat 2 more minutes on medium speed, scraping bowl occasionally. Pour batter into pan.
2Bake 30 to 35 minutes or until toothpick inserted in center comes out clean. Cool completely in pan on cooling rack, about2 hours.
3Place bittersweet chocolate in medium heatproof bowl; set aside. In 1-quart saucepan, heat 1 1/2 cups whipping cream to simmering. Remove from heat; stir in 1/2 teaspoon red pepper. Let stand 10 minutes. Return whipping cream in saucepan to simmer. Pour over bittersweet chocolate. Let stand 2 minutes; stir until smooth. Spread ganache over cake. Refrigerate until set, about 1 hour.
4Place white chocolate in medium heatproof bowl. In 1-quart saucepan, heat 1 cup whipping cream to boiling. Pour over white chocolate. Let stand 2 minutes; stir until smooth. Spread evenly over bittersweet ganache. Drizzle decorating gel in rows over cake. Pull toothpick through rows in opposite direction to create swirled pattern. Refrigerate at least 4 hours or overnight.