Preheat oven to 190 degrees C. Grease and flour twenty-four Madeleine moulds.
In a medium bowl beat eggs, vanilla and lemon zest with an electric mixer on high speed for 5 minutes. Gradually beat in the icing sugar. Beat for 5 to 7 minutes or until thick and satiny.
Sift together the flour and baking powder. Sift one quarter of the flour mixture over the egg mixture, gently fold in. Fold in the remaining flour by quarters. Then fold in the melted and cooled butter. Spoon batter into the prepared moulds, filling 3/4 full.
Bake for 10 to 12 minutes or until the edges are golden and the tops spring back. Cool in moulds on a rack for 1 minute. Loosen biscuits with a knife. Invert biscuits onto a rack and cool. Sift icing sugar over the tops or melt semi-sweet chocolate chips and dip the tips in the chocolate. Store in an airtight container.