To make the cookies, add the soft butter and granulated sugar to a large mixing bowl, and use a hand mixer to beat them well until creamy.
Crack in the egg and beat again.
Sift in the flour, add the vanilla extract, and use your hands to knead it into a dough.
Cover the dough with clingfilm and refrigerate for 20 minutes.
Preheat the oven to 180 degrees.
Roll the dough using a rolling pin, and use flower-edged cookie cutters to cut out shapes.
Line 2 baking trays with non-stick paper and arrange the cookies onto them - I got 20 cookies.
Bake for 10-12 minutes until the edges of the cookies are slightly golden.
Remove the cookies from the oven and allow them to cool down completely.
To make the icing, sift the icing sugar in a bowl, add the milk and use a spoon to mix them into a smooth paste.
Add the food colouring, and mix well to have a uniform colour.
Once the cookies have cooled down, add a teaspoon of the icing onto each cookie, making sure you don't spread it too close to the edges, and decorate with smarties.
Allow the icing to set before serving.