Cream the butter and sugar in the bowl of an electric mixer fitted with a paddle attachment, working on low to medium speed, until the mixture is well combined.

Add the egg and milk, then mix until smooth. Sift the flour and cocoa powder together, add them to the bowl, and mix again. The dough is ready when it starts to gather around the paddle attachment.

Roll the dough into a 6 mm – ¼ inch thick sheet and cut out the cookies using a cardboard stencil. You can make your own stencil by printing the image you want to use, placing transfer paper between the printout and a clean piece of cardboard, tracing the outline with a pen, and cutting out the shape with a sharp craft knife.

Arrange the cookies on a baking tray lined with baking paper and decorate them with M&M’s. For the whiskers, press the dough gently with the prongs of a fork.

Bake in a preheated oven at 180°C – 355°F for 15 minutes.

Leave the cookies to cool on the baking tray for a few minutes, then transfer them to a wire rack to cool completely.