3 cups flour, plus more for counter
2/3 cup unsweetened cocoa
3/4 tsp salt
1/2 tsp baking powder
16 T unsalted butter, softened
1 1/2 cups sugar
2 large eggs
1 tsp vanilla
Preheat oven to 350 degrees. Whisk the flour, cocoa, salt, and baking powder together in a bowl, and set aside. Beat butter and sugar with electric mixer until fluffy. Add eggs, one at a time, scraping down bowl. Mix in vanilla. Gradually mix in the dry ingredients. Wrap in plastic, and chill for at least 1 hour.
Roll out the cookie dough on a floured counter. Cut into desired shapes, brushing extra deposits of flour off the top. Bake on a parchment-lined baking sheet for 8-11 minutes (the former for 1/8-inch cookies, the latter for 1/4-inch cookies), until the edges are firm and the centers are slightly soft and puffed. Cool on a wire rack.