Preheat oven to 180°C and place the flour, sugar, cocoa and baking powder in a bowl and stir to combine.
Place buttermilk, egg, oil, and vanilla in a separate jug then mix into the dry ingredients. Beat well to combine.
Line a muffin pan with paper muffin cases and divide mixture between them.
Push chocolate sauce into the centre of each cupcake and ensure it is completely covered with batter. (Recipe for Bar-One chocolate sauce
Bake for 20 minutes. Set aside to cool.
Meanwhile, place dark chocolate, chocolate sauce and cream in a bowl over simmering water until chocolate melts. Set aside to cool slightly. Use an electric beater to beat until smooth.
Spread over cupcakes and top with gold leaf.Recipe reprinted with permission of Nestlé®.