1. Break the chocolate into small pieces in a bowl. Melt it in a bain-marie. Remove from heat. Add the butter in small cubes and stir.
2. Separate the egg whites from the yolks. Beat the egg whites until stiff and place in the fridge.
3. In a bowl, mix the egg yolks and dulce de leche. Add to the melted chocolate and stir until the mixture is homogeneous.
4. Gently incorporate the beaten egg whites with a spatula to keep the mousse texture.
5. Transfer to glasses and refrigerate for 3 hours.
6. Before serving, garnish with dried bananas.