makes about 3 dozen cookies
For the cookie wafers:
1 cup unsalted butter, room temperature
1 cup powdered sugar
1 teaspoon vanilla extract
1 egg white
1 cup unsweetened (and non-alkalized) cocoa powder (I used Ghiradelli unsweetened cocoa powder)
3/4 teaspoon fine grain sea salt
1 1/2 cups whole-wheat pastry flour
For the chocolate-peppermint coating:
16 ounces dark chocolate melting wafers (I used Ghiradelli brand)
1 1/2 teaspoons organic peppermint extract
1. Preheat the oven to 350 degrees. Line a baking sheet with parchment paper or a silpat and set aside.
2. Using an electric mixer with the paddle attached, cream the butter until light and fluffy. Add in the powdered sugar and cream until smooth, scraping down the sides of the bowl as necessary. Stir in the vanilla, egg white, salt, and cocoa powder.
3. Mix in the flour until it is just incorporated -- the dough should be smooth and not grainy or powdery in appearance.
4. Turn the dough out onto a lightly floured work surface. Knead the dough a few times to form a ball.
5. Place the dough in the center of a sheet of plastic wrap and flatten it into a disk. Cover the dough with the plastic wrap and freeze for 20 minutes.
6. After the dough has chilled, use a rolling pin to roll it out into about 1/4" thickness. To prevent the dough from sticking to the rolling pin, it helps to sandwich the dough between two sheets of plastic wrap.
7. Use a round or fluted 1 1/2-inch cookie cutter to cut out the cookies and place them on the prepared baking sheet. (I baked my cookies in three separate batches.)
8. Bake the cookies in the oven for about 10 minutes. Heidi suggests baking them until "they smell of deep warm chocolate, with toasty overtones" -- you'll understand what she means when you bake them.
9. Remove the baked cookies from the oven and let them cool completely on a wire rack.
10. While the cookies are cooling, prep the chocolate coating.
11. Melt the chocolate, either in the microwave in 30 second increments (stirring in between) or with a double boiler. Stir in the peppermint extract.
12. Cover a clean baking sheet with a sheet of parchment paper. Carefully dip each cookie into the melted chocolate (I used a fork) and gently turn the cookie to cover it entirely in chocolate. Gently shake the cookie to allow any excess chocolate to drizzle off before placing the coated cookie on the prepped baking sheet.
13. After all the cookies have been dipped in the chocolate, place the baking sheet with the cookies into the fridge or freezer to set the chocolate.
14. The thin mint cookies can be stored in an airtight container kept at room temperature or in the freezer.