Add the butter and sugar to a food processor. Pulse at medium-high speed until well combined.

First, add the whole egg to the creamed mixture with the food processor running, and beat until combined. Then add the egg yolk and vanilla and beat until well combined.

Sift together the flour, cocoa powder, and salt.

Add the dry ingredients to the egg and butter mixture all at once. Pulse until a dough forms, do not overmix.

Remove the dough from the food processor, cover it in plastic wrap, and refrigerate for an hour.

Remove the chilled dough from the fridge and roll it out on a floured work surface to a thickness of ½ cm ( ¼ inch) using a rolling pin.

Cut about 50 circles out from the dough using a round 10cm diameter cookie cutter and place the cookies onto an oven tray lined with parchment paper. Bake in a preheated oven for 12 minutes or until the cookies are baked. Allow the cookies to cool on a cooling rack.

In a bowl of an electric mixer fitted with a paddle attachment, add the butter and icing sugar. Beat at medium speed until the mixture looks like fine breadcrumbs.

In a jug combine the milk and vanilla, with the mixer's motor running at low speed slowly add the milk mixture. Continue until it has all been added. Then increase the speed of the mixer to medium-high. Beat until light and fluffy, scraping down the sides of the bowl often.

Separate the frosting into three bowls, and colour each bowl of frosting a different colour.

Add the coloured frosting to three separate piping bags.

Pipe a dollop of frosting onto half of the cooled cookies, then place a plain cookie on top of this to create a cookie sandwich.

Decorate the cookies with edible spooky eye sprinkles, serve and enjoy!