This is an improved version of Mary Berry’s tip on butter. She suggests using a grater to cut butter before using it in a dough recipe. My tip goes a bit further, making it just perfect! All you need to do is first slice the butter into slices then you can use the grater cutting across making very small pieces of butter. Then, quickly combine the small pieces of butter with the flour and sugar.
Here is are couple of pictures to illustrate what I mean: