Start with the chocolate sauce, bring the milk and cream to the boil in a small saucepan. Place the chocolate pieces into a bowl. Pour over two-thirds of the milk and cream mixture, stirring until melted and smooth.
Place the vanilla seeds into the mascarpone and whip until combined. Fold meringues and banana slices into the cream, leaving a few slices of banana for garnish. Place in a cup and drizzle with chocolate sauce. Top with remaining banana slices. Serve immediately.