Preheat oven to 350 degrees F. Line two very extra-large cookie sheets with parchment paper. Draw two 6-inch circles on the parchment paper on each cookie sheet, leaving 3 inches between the circles. Turn paper over so the ink is on the bottom of the paper; set aside.

In a large bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Add granulated sugar, brown sugar, baking soda, and salt. Beat until well combined, scraping bowl occasionally. Beat in eggs and vanilla until combined. In a medium bowl, stir together flour and cocoa powder. Add flour mixture and milk alternately to butter mixture, beating on low speed after each addition just until mixture is combined.

Spoon dough evenly on top of circles on prepared cookie sheets. Spread the dough evenly on layers in each circle. Bake in the preheated oven about 15 minutes or until cookies are set. Cool completely on sheets on wire racks.

Using a large spatula, invert one of the cookies onto a serving platter. Spread with half of the Creme de Menthe Filling. Top with another cookie, flat side down. Repeat with remaining cookies and filling. With a serrated knife, cut each whoopie pie into 16 wedges. (Eat wedges with a fork.) If desired, top wedges with chopped candies. Makes 32 sandwich cookies.

In a large bowl, beat 1/2 cup softened butter with an electric mixer on medium to high speed for 30 seconds. Gradually beat in 1 cup powdered sugar. Beat in 2 tablespoon creme de menthe* (or 2 tablespoons milk, 1/2 teaspoon mint extract and several drops green food coloring) and 1 tablespoon milk. Gradually beat in another 5 cups powdered sugar. Beat in 3 to 4 tablespoons additional milk to make a filling of spreading consistency. Makes 3-1/4 cups.

If using clear creme de menthe, add several drops of green food coloring to the filling.

Layer cookie wedges between sheets of waxed paper in an airtight container; cover. Store in the refrigerator for up to 3 days or freeze for up to 3 months.