oil, eggs and water as directed on cake mix package
For the coconut sauce:
3cupsflaked sweetened coconut
For the chocolate frosting:
4 1/2tablespoonscocoa powdersifted
2and 1/2 cups powdered sugar
For the cake: Coat a 9"x13" pan with cooking spray. Prepare the cake mix with the oil, eggs and water in amounts as directed on the box and bake according to package instructions. Cool completely in the pan.
For the coconut sauce: Combine milk, sugar and marshmallows in a medium saucepan, cook over medium heat for 5 minutes or until the marshmallows are melted.
Stir in coconut and cornstarch, bring to a boil. Cook one minute, stirring constantly. Remove from heat and pour the coconut sauce over the cake while it's still warm, then let cool completely before you add the frosting.
For the frosting: Melt butter in a small, heavy saucepan over low heat. Add granulated sugar, milk and cocoa powder, cook for 2-3 minutes or until mixture is thoroughly combined.
Remove from heat and cool slightly. Stir in powdered sugar and vanilla. Pour over the cake. Add the sprinkles on top while the frosting is still warm. Do not try to spread the frosting with a knife or it will not set properly.
Make Ahead: The entire cake can be made a day in advance.Little Helpers: Sprinkle time! Let your kids do the decorating