In a saucepan combine all the ingredients and stir.
Bring to a boil on medium-high heat and stir until bubbling. Remove from the heat and pour on top of the warm cake. Spread the frosting to cover the entire cake.
Turn the oven onto broil and return the cake to the oven on the top rack just under the broiler. Leave the oven door cracked open so you can watch the cake. Don’t walk away as this happens quite fast and you don’t want to burn the frosting. When the frosting starts to bubble, take the cake out and serve it warm.