Preheat oven to 350F. Grease and flour, or spray madeleine molds. Melt butter and chocolate in saucepan over low heat; stir to blend. Sift cocoa powder, sugar, flour and slat into medium bowl. Beat or whisk eggs, egg yolks and vanilla in small bowl until light and fluffy. Blend melted chocolate mixture and eggs into flour mixture. Stir until sugar is well incorporated (about 2 minutes). Fill each mold 1/2 full. Lightly tap pan so that tops are all flat. Bake in oven for 5 minutes or until centers are done. Remove to wire racks, shell side up to cool. As cakes cool, place in airtight container to prevent drying out.

Prepare Butter Cream Filling. Cream butter, sugar and vanilla until well incorporated. Add enough milk to make a spreadable filling. Spread 1 1/2 teaspoons of filling between each pair of cakes (flat sides) and mound more to top so it gives the effect of an opened sea shell. Refrigerate in a covered container to firm filling. Brush melted chocolate on top side of each cookie presentation. May be frozen. Let stand about 15 minutes at room temperature.

Or:

Fill molds 2/3 full and bake madeleines about 10 minutes until centers test done. Dip narrow ends in melted chocolate or brush tops with chocolate to coat. These would also be pretty dusted with ground chocolate over the wet chocolate icing.