Black Forest Mug Cake

Ingredients

• 2 tablespoon butter
• 1 1/3 ounce dark chocolate, broken into small pieces
• 1 medium egg, lightly beaten
• 2 tablespoon 2-percent milk
• 3 tablespoon superfine sugar
• 3 tablespoon all-purpose flour
• ¼ teaspoon baking powder
• pinch of salt
• 1 tablespoon cherry jam
• ¼ cup heavy cream
• 1/3 ounce dark chocolate
• fresh cherry, to garnish