1. Heat oven to 325 degrees F and place rack in center. Line one baking sheet with parchment paper. In a medium bowl, whisk together flour, cocoa, baking soda and salt; set aside. In a medium saucepan, melt together chocolate and butter over medium heat, stirring occasionally. Let stand until cool, about 20 minutes. Stir in sugar and extract until combined. Stir in eggs until combined well. Add flour mixture and stir until a soft dough forms.
2. Roll cookies into 3/4-inch balls. Dip tops in nonpareils and place, coated side up, 1 inch apart on prepared sheet. Bake until set but not firm to the touch, 10 to 13 minutes. Using a metal spatula, transfer cookies to a wire rack and let cool completely.
3. Meanwhile, prepare Peppermint Marshmallow. Transfer half to a large decorating bag fitted with a 1/2-inch plain tip or coupler. Pipe mounds, about 1/2 inch high, on flat side of half of the cookies. Top with remaining cookies, making sandwiches. (Can be made ahead. Store in an airtight container at room temperature, in single layers separated by waxed paper, up to 2 days.) Makes 48 sandwich cookies.
1. In a large mixer bowl, sprinkle gelatin over cold water and let stand until softened, about 5 minutes. Meanwhile, in a small saucepan, combine sugar and water. Stir over medium-high heat until sugar dissolves. Using a pastry brush dipped in water, brush down sugar crystals on sides of pan. Place a candy thermometer into mixture. Boil (do not stir) until syrup registers 238 degrees F (soft-ball stage), about 10 minutes. Pour into gelatin. Using the whisk attachment, beat gelatin mixture on medium-low speed until slightly cooked, about 5 minutes. Increase speed to medium-high and beat to soft peaks, about 12 minutes. Stir in peppermint candies until combined. Tint with food coloring (if desired). Use immediately. Makes 4 cups.