Jamocha Rum'n Butter Cake

• 1 hershey bar
• 475 ml whipping cream
• 120 gr rum
• 120 ml water
• 100 gr sugar
• 28 gr butter
• 16 gr instant coffee
• 16 gr instant coffee powder
• 1 package devils food cake mix with pudding
• 1 package chocolate fudge frosting mix