Cream
the butter and sugar until light and fluffy. Sift
in the 2 flours and mix well to combine.
Press
the mixture into an oblong tin about
30 x 20 cm/12 x 8 inches and
mark with the tines of a fork.
Bake in a
preheated
oven, 140°C (275°F), Gas Mark 1, for 30 minutes, then
reduce the
temperature to
120°C (250°F), Gas Mark 12 and cook for a further 1-1
1/2
hours.
Remove the shortbread from the oven and cut into
32
fingers. Sprinkle with caster sugar and leave to cool
slightly in the tin before transferring to a wire rack
to cool completely. Store in an airtight tin.