Servings: Makes 72 cookies
Ingredients 1 1/2 cups all-purpose flour1/2 cup unsweetened cocoa powder1 1/4 cups sugar1/2 tsp. baking powder1/4 tsp. baking soda1/4 tsp. salt6 ounces (1 1/2 sticks) cold unsalted butter , cut into 1/2-inch pieces2 large egg yolks1 1/2 tsp. peppermint oil1/4 tsp. vanilla extract1 1/2 pounds bittersweet chocolate
Place the flour, cocoa, sugar, baking powder, baking soda, and salt in a food processor fitted with the steel blade and pulse a few times to combine the ingredients. Add the butter and pulse to cut the butter into the dry ingredients. Add the egg yolks, peppermint oil, and vanilla and pulse until a dough forms on the blades of the food processor.
Remove the dough from the food processor and shape into a 2-inch-thick log. Wrap in plastic wrap or parchment paper and refrigerate for at least 2 hours, or overnight.
Place racks in the middle and lower third of the oven and preheat the oven to 350°F. Line baking sheets with parchment paper.
Remove the dough from the refrigerator. Cut into 1/4-inch-thick disks and arrange 1/2 inch apart on the baking sheets. Bake for 10 minutes. Switch the baking sheets from top to bottom and rotate from front to back and continue to bake for another 3 to 4 minutes, until the cookies are light brown. Remove from the oven and allow to cool on racks. Make sure to let the baking sheets cool between batches. Do not handle the cookies until they are cool, or they'll break; they're very delicate.
Melt and temper the bittersweet chocolate. Keep the chocolate warm while you dip the cookies.
Place a sheet pan upside down on your work surface, next to the melted chocolate. Cover with parchment paper. Dip the cookies one by one in the chocolate, using a fork to turn them over and then lift them out of the chocolate. It helps to tilt the bowl forward by leaning it on a folded kitchen towel.
Set the dipped cookies on the parchment, beginning at the far end so you don't drip chocolate on other cookies when you set them down. Allow to cool completely, then store in an airtight container.