I originally found the recipe over at BakeBakeBake (a community on Livejournal). It's a great place to browse for fun recipes and it's full of super talented bakers. Definitely check it out if you get the chance.
2 cups flour
1/2 cup cocoa powder
1 cup powdered sugar
2 sticks butter
1/4 tsp salt
1 tsp vanilla extract
(Depending on how big you make your cutouts, this should yield about 24-30 cookies.)
1. Preheat oven to 300º F
2. Cream butter. Add in sugar, salt, and vanilla extract. Mix until smooth.
3. On low speed, add the flour and cocoa powder until the dough holds together.
4. Form mixture into a ball and flatten slightly.
5. Flour your work surface and rolling pin. Place the dough onto the floured surface, coating both sides, and roll the dough out until it's about 1/2 an inch thick.
6. Use a circular cookie cutter or other round object to cut the dough into about inch to 1 1/2 inch circles. Prick the surface with a toothpick to create buttonholes.
7. Bake for 25-30 minutes.