In the bowl of a stand mixer, whisk together flour, cocoa, confectioners’ sugar, and salt. Add cold butter; using the paddle attachment, beat at low speed until mixture resembles coarse meal. Add egg and egg yolk; beat until combined and a dough forms.

Turn out dough, and shape into a disk. Wrap in plastic wrap, and refrigerate until firm, at least 2 hours. Let stand at room temperature for 10 to 15 minutes before rolling out.