Bittersweet Chocolate Walnut Moons

1/4 pound unsalted butter, room temperature
3/4 cup toasted walnuts, finely chopped
1/3 cup sugar
1/2 cup unsweetened cocoa powder
1 cup flour
1/4 teaspoon vanilla

Place butter, walnuts, sugar, cocoa powder, flour and vanilla in bowl of a mixer fitted with a paddle and mix until the dough just comes together. Cover with waxed paper or plastic wrap and refrigerate at least 2 hours, or freeze up to 2 weeks.

Preheat the oven to 300ºF. To make crescent moons: form the dough into 1" balls and flatten with your hand. Place on ungreased cookie sheet. Transfer to oven and bake until golden brown, about 15-20 minutes.

Cool for 2 minutes and then remove to a rack and sprinkle with powdered sugar.