By Kit Chapman
Sieve the flour into a bowl and mix in the oats. Add the soft butter pieces, spreading them all over the dry mixture, and work in lightly with your fingers. Once the butter has been roughly absorbed – it is important that you do not overwork it – it will get rather wet and sticky to the touch.
Fold in the icing sugar along with the orange zest. Zig-zag the egg yolks over the mixture, an