Place butter and confectioners' sugar in a mixing bowl. Using the paddle attachment, mix together until mixture is smooth and pale (note: a hand mixer may also be used)
¾ Cup unsalted butter, softened, ¾ Cup confectioners' sugar, sifted
Add egg and mix well.
1 large egg, room temperature
Add cocoa powder and flour. Mix until the dough starts to come together (it will appear crumbly).
Empty dough onto a work surface. Knead a few times until the dough comes together. Wrap in plastic and refrigerate for 1 hour before using. Note: if making a 'press in crust' the dough may be used immediately.
To roll out dough: sprinkle work surface with flour and roll dough to desired thickness.