Chocolate cupcakes with truffles spread icing - Le Coup de Grâce

Ingredients

• 1/3 cup butter, room temperature
• 3/4 white sugar
• 1 tablespoon dark rum
• 1/3 cup 5% sour cream
• 90g 72% dark chocolate, finely chopped
• 3 egg whites
• 1 1/4 all purpose flour
• 2 tablespoons baking powder
• 2 pinches salt
• 1/3 cup dark chocolate milk
• About 15 cacao truffles with hazelnuts chunks from Trufettes de France
• 1/2 cut salted butter, room temperature
• 1/2 cup vegetal shortening
• 4 cups icing sugar
• 1/2 cup truffles spread
• 5 tablespoons milk