Mix butter and sugar until smooth and easily spreadable.
Add flour and mix until it comes together. Don't overmix.
Press into a ball.
Reserve a small amount of dough for colouring (like a generous pinch! You end up needing less than you think).
Roll out the plain dough like in the video.
To make the piping paste, mix some leftover shortbread (1-2tsp) with black food dye and enough egg white or aquafaba to make it a pipeable consistency.
Put in piping bag, pipe it!
Cut out shapes, chill in fridge/freezer before baking, and bake for 12 mins at 160C/325F (fan).
Cool on wire rack.
