a piping bag fitted with a large French pastry tube
Level off the smooth side of each of the madeleines by shaving off the humps with a serrated knife. Mix the frosting, confectioners' sugar and a little pink food coloring in a medium bowl; stir until a consistent pink is achieved. Transfer the frosting to a piping bag fitted with a large French pastry tube. Pipe a swirl of frosting on the flat side of a madeleine, then sandwich with another, flat sides facing in, so the shape mimics an oyster. Repeat with the remaining cookies and frosting. Place a shimmery candy-coated chocolate in the frosting of each assembled cookie.
Crumble the brown sugar in a sandy layer across the bottom of a shallow bowl. Arrange the cookie oysters on top.