Preheat oven to 375 degrees F. Line a cookie sheet with parchment paper; set aside. In a large bowl, beat the 1/2 cup butter with an electric mixer on medium to high speed for 30 seconds. Add the brown sugar, cocoa powder, baking soda, and salt. Beat until combined, scraping bowl occasionally. Beat in egg and vanilla until combined. Alternately add flour and buttermilk, beating on low speed after each addition just until mixtures are combined. Stir in red food coloring.

Spoon dough with a rounded teaspoon measure batter 2 inches apart onto prepared cookie sheet. Bake in the preheated oven for 7 to 9 minutes or until edges are set. Cool on cookie sheet for 2 minutes. Transfer cookies to a wire rack; let cool.

Spread Peppermint and Cream Cheese Filling on bottom of each of half of the cookies. Top with remaining cookies, flat sides down, pressing lightly together.

Serve cookies immediately. If chilled, let stand at room temperature for 15 minutes before serving. If desired, sprinkle each cookie with some finely chopped peppermint candies before serving. Makes about 40 sandwich cookies.

In a large bowl, combine two 3-ounce packages cream cheese, softened; 3 tablespoons butter, softened; and 1/2 teaspoon peppermint extract. Beat with an electric mixer on medium speed until light and fluffy. Gradually beat in 3 cups powdered sugar. If necessary, add milk (1 teaspoon at a time) to make a filling of spreading consistency.

Layer cookies between sheets of waxed paper in an airtight container; cover. Store in the refrigerator up to 3 days.