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)
Add egg and mix well.
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.