Add the butter, powdered sugar, vanilla extract, and egg yolk into a mixing bowl, then beat together with a wooden spoon until creamy (or mix in a food processor until well combined).
Sift the flour and salt together in a separate bowl and add the ground almonds.
Now add the flour and almonds mixture slowly to the sugar butter mixture and beat until everything just comes together to form a dough. Take care not to over mix it.
Shape the dough into two flat rounds and wrap in cling film. Chill in the fridge for 20/30 mins. Preheat the oven to 350°F and line two baking sheets with non-stick baking parchment. Turn the dough out onto a lightly floured work surface and roll out to ¼ inch thick.
Cut Christmassy shapes like stars out of the dough using Christmas cookie cutters. When you've made your first set of cookies, gather the leftover pastry cuttings and bring them together. Dust the worktop with more flour and roll out the pastry again to make as many cookies as possible until the pastry is all used up. Place the cookies onto the lined baking sheets, leaving a little space between each one, and bake in the oven for 10/12 minutes until a light golden colour. Allow the cookies to cool on the tray.
Meanwhile, mix some sieved powdered sugar with a few drops of cold water to make a thick icing. Spread or pipe it over the cooled biscuits and decorate with edible silver balls. These can be packed in cellophane bags and tied with ribbons to be given as a nice Christmas gift!