In a large bowl, cream together the butter, sugar and vanilla until light and fluffy (I use an electric mixer but this can be done by hand).
Add in the flour, cocoa powder and salt and stir until combined; to bring it together into a ball of dough, add the plant milk and stir.
Lightly dust your work surface with flour and tip the dough out (don’t worry if its still crumbly at this stage, there’s no need to add extra milk).
Knead the dough to bring it together until its one smooth ball of dough. Avoid overworking it.
Wrap the dough in cling film or place it into a Ziploc bag and place into the fridge to chill for at least 30 minutes. While the dough is cooling, line a couple of baking sheets with baking paper and place to one side.
Once the dough is chilled, roll it out on to a floured surface. Be sure to move pick up the dough and rotate in between rolling it out to stop it sticking to your work surface. Stop once the dough is roughly 5mm / ¼ inch thick.
Cut out as many cookies as you can and place them straight on to the lined baking trays. Place these trays into the fridge for 30 minutes.
Bring together all of the trimmings into a ball, re-roll and cut out more cookies. Keep repeating this until you have use up all of the dough and don’t forget to chill them before baking.
While the cookies are chilling, preheat the oven to 180 C / 350 F / gas mark 4.
Bake the cookies for 12-15 minutes until they are just golden brown.
Once baked, transfer the cookies to a cooling rack and leave to cool completely before decorating