½ cup Dutch-processed cocoa powder
2 tsp baking powder
1 cup (2 sticks) salted butter, cut into chunks
1 cup granulated sugar
1 tsp pure vanilla extract
2 oz bittersweet chocolate, melted and cooled
For the glaze:
1 cup Dutch-processed cocoa powder
3 ½ cups powdered sugar
4 Tbsp light corn syrup
6 Tbsp milk
Whisk the flour, cocoa powder, and baking powder together. Set aside. Cream together the butter and sugar until light and fluffy. Add the egg and vanilla; beating until combined. Scrape the bottom and sides of the bowl as necessary. Beat in the melted chocolate. Add the flour mixture in 3 parts, beating on low after each addition. Beat just until the dough comes together. Pat into 2 discs, wrap in plastic wrap and chill for 30 minutes.
Preheat oven to 350°F. Line 2 cookie sheets with parchment paper.
Roll the dough on a surface lightly coated with a mixture of flour and cocoa to about a ¼” thick. Cut with a 2″ round cookie cutter. Place the cut-outs on a prepared baking sheet and place in the freezer for 5-10 min. (This will prevent spreading.)
Bake the cookies for about 9 minutes, or until done. Remove to a wire cooling rack to cool completely.
For the glaze:
In a medium bowl, whisk the cocoa powder and powdered sugar together. Add the corn syrup and milk, whisking until smooth. The glaze will be very thick, but still pourable. Transfer to a piping bag, fitted with a #12 tip, or to a zip-top bag and snip the corner.
Pipe the glaze in a circle onto the cookies. The glaze will spread, so don’t go too close to the edges. If some spills over the edge, it’s ok.
Let the cookies dry for at least one hour before adding the white squiggle.