In a medium mixing bowl, whisk together the dry ingredients; flour, cocoa powder, baking soda, baking powder, and salt until well combined.

Cream together the butter, shortening, and sugar in a stand mixer on medium speed until light and fluffy.

Melt the chocolate in a microwave-safe bowl and add to the butter mixture, mixing thoroughly until combined.

Add eggs one at a time to the mixture, along with the vanilla extract and mix again until smooth.

Gradually add the dry mixture to the wet ingredients while mixing on low speed until just combined.

Wrap the dough in plastic wrap and refrigerate for at least 1 hour.

Preheat your oven to 375°F (190°C) and line baking sheets with parchment paper.

Roll the dough out to about ¼-inch thickness and cut out circles with a cookie cutter.

Bake the cookie rounds for 10-12 minutes and allow to cool on sheets before transferring to a wire rack.

In a stand mixer, combine confectioner’s sugar, corn syrup, shortening, milk, and peppermint extract until smooth.

Fold in crushed peppermints into the filling mixture.

Spread the mint filling on one cookie and press another on top to create a sandwich.