Preheat oven to 350°F. Prepare Mini Whoopie Pie Pan with vegetable pan spray.

In large bowl, sift together flour, cocoa, baking powder, baking soda and salt.

In large bowl, beat butter and sugar with electric mixer until light and fluffy. Add egg and vanilla; beat until well combined. Alternately add flour mixture and buttermilk in three additions, beating until just combined. Spoon two teaspoons batter into each pan cavity.

Bake 6-8 minutes or until tops of cakes spring back when touched. Cool in pan 3 minutes. Remove and cool completely on cooling grid.

In small bowl, melt 3/4 cup Candy Melts candy according to package instructions. Using spatula or butter knife, spread small amount of melted candy on bottom of each whoopie pie. Set aside until candy is set.

For icing, beat butter and shortening with electric mixer until light and fluffy. Gradually add sugar, one cup at a time, beating well on medium speed. Scrape sides and bottom of bowl often. When all sugar has been mixed in, icing will appear dry. Slowly add milk; beat at medium speed until light and fluffy.

In medium bowl, melt remaining candy melts according to package instructions. Cool slightly. Beat candy into icing with electric mixer until well combined, scraping bottom and sides of bowl often.

To assemble, using open star decorating tip 22, pipe a large rosette onto one whoopie pie. Top with second whoopie pie to create a sandwich. Sprinkle sides with sugar if desired.