Preheat oven to 250°F. Using the straight side of the round cut-out C (2 in.) from the Round Double Cut-Outs Set, trace 36 circles onto parchment paper. Flip parchment over and place on cookie pan.
In large bowl, whip Meringue Powder, water and salt with electric mixer on high speed until soft peaks form. With mixer running, gradually add sugar and 1/2 teaspoon vanilla. Whip until stiff peaks form and mixture triples in volume. Reduce speed to low and add 1/4 cup cocoa powder, scraping down bottom and sides of bowl as necessary and beating until well combined.
Using a decorating bag fitted with tip 1A, pipe meringue about 1/4 to 3/8 in. thick over the traced circles as a guideline. Flatten points with tip of finger.
Bake 35-40 minutes or until outsides of meringues feel firm and crisp. Cool completely on pan.
In large bowl, whip cream and confectioners' sugar on high speed until very soft peaks form. Add Piping Gel, remaining 1 teaspoon vanilla and remaining 1/4 cup cocoa powder; whip until stiff peaks form, scraping down bottom and sides of bowl as necessary. Place in decorating bag fitted with tip 1M.
To assemble merveilleux, pipe a rosette of chocolate whipped cream to cover 12 of cooled meringues. Top with a second meringue and repeat with whipped cream. Invert remaining meringues flat sides up and press into whipped cream. Freeze merveilleux at least 30 minutes. Refrigerate remaining whipped cream.
Remove half of the merveilleux from freezer for icing; keep other half in freezer. Spread a very thin layer of chocolate whipped cream over the sides of the merveilleux. Roll in chopped Candy Melts Candy to cover. Using a decorating bag fitted with tip 1M, cover top with a rosette of chocolate whipped cream. Repeat with remaining frozen merveilleux.
Refrigerate at least 3 hours before serving to allow meringue cookies to soften. Merveilleux are best eaten within 24 hours so the meringue cookies maintain some of their crisp, chewy texture.