Preheat oven to 180 degrees C. Empty cake mix into a bowl. Add mousse mix and stir to combine. Add sparkling wine, eggs and butter. Stir until combined.Stir in broken chocolate.
Divide mixture among a 6-hole Texas (very large) muffin tin (3/4-cup capacity) lined with large muffin cases if you like.
Cook in a preheated oven for about 25 minutes or until cooked when tested with a skewer. Transfer to a wire rack to cool.
To make the chocolate cream, whip the cream in a small bowl with electric mixer until firm peaks form. Add chocolate topping, beat until combined.
To decorate the muffins, trace a small heart-shape onto a piece of paper, cut around the shape, then remove it. Place the piece of paper from which the heart-shape was cut onto each muffin and dust a heart shape with sifted icing sugar.
Serve muffins warm or cold with chocolate cream and berries.