Preheat oven to 375°. Line baking sheets with parchment paper.

For cookies: In a medium bowl, whisk together flour, cocoa, salt, baking powder, and baking soda.

In a large bowl, beat butter and granulated sugar with a mixer on medium speed until fluffy. Add eggs, one at a time, beating until combined. Beat in vanilla.

Gradually add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture, and beating just until combined after each addition.

Using a 1-tablespoon spring-loaded scoop, scoop batter 2 inches apart onto prepared pans. Bake until top and edges are set, 8 to 10 minutes. Let cool on pans for 5 minutes. Remove from pans, and let cool completely on wire racks.

For filling: In a medium bowl, beat marshmallow crème and butter with a mixer on medium speed until smooth and combined. Beat in confectioners’ sugar, extracts, and salt until smooth and well combined, stopping to scrape beaters and bowl. Stir in half of crushed peppermint bark.

Spread 1½ to 2 tablespoons filling onto flat side of half of cookies. Top with remaining cookies, flat side down, gently pressing until filling reaches the edges. Roll edges in remaining crushed peppermint bark. Refrigerate in an airtight container for up to 5 days.