Buttery Shortbread Swirls

These are beautifully delicate gifts for the family, looking and tasting great. I would, however argue that, for ordinary shortbread consumption, this isn't the tastiest recipe to use, as themixturehas to be piped without crumbling. Still, fresh from the oven or even kept in an airtight container or frozen, they are very nice. Don't be tempted to add more milk for ease of piping - theywon't hold their shape in the oven. Recipe from Fifteen Spatulas. Makes 25-30 swirls.
Ingredients:
-220g butter, softened 
-110g icing sugar
-1 tsp vanilla extract
-285g plain flour
-1 tbsp milk