• Heat oven to 350°F. Spray bottom of 13x9-inch pan with cooking spray
• In large bowl, beat cake mix, water, oil and eggs with electric mixer on medium speed 2 minutes, scraping bowl occasionally. In small bowl, pour 1 ¼ cups of the batter; stir in 2 tablespoons cocoa until blended. In another small bowl, pour 1 ¼ cups of the batter; stir in 2 tablespoons strawberry jam and ¼ teaspoon food color until blended. Pour remaining cake batter in bottom of pan. Drop tablespoons of each colored batter in random pattern over top; pull table knife through batter to make swirls.
• Bake 28 to 30 minutes or until toothpick inserted in center comes out clean. Cool completely, about 1 hour

Frosting

• In large mixing bowl, beat softened butter with electric mixer on medium-high speed until smooth. On low speed, gradually beat in powdered sugar until smooth and creamy. Beat in 2 tablespoons milk and the vanilla. If frosting is too stiff to spread, add additional milk, 1 teaspoon at a time.
• In small bowl, pour ¼ cup of the vanilla frosting; stir in 1 teaspoon strawberry jam until blended. Stir in food color until desired color. In another small bowl, pour 3 tablespoons of the vanilla frosting; stir in 1 teaspoon cocoa until blended. Spread remaining vanilla frosting on top of cake. Randomly drop measuring teaspoonfuls of strawberry and chocolate frosting over top. Use small icing spatula to swirl frosting over top of cake. Store loosely covered at room temperature.