I blitzed butter and flour quickly in a food processor then poured into a bowl, add icing sugar. Can mix with fingers to a fine breadcrumb.
Beat egg and milk together. Make a well in the centre of the flour and pour in the eggy milk, stirring with a knife. Add a little more milk if need be to pull it all together, give all a hand squeeze.
Wrap pastry into some cling film and pop in fridge for use this day. You can also portion, warp firmly in cling wrap and pop into a labelled bag to freeze for use another day.