Preheat the oven to 180C/350F/Gas 4 Line a baking sheet
Sift the flours into a nice big bowl so you have room to work and make a well in the centre.
Put the sugar in the middle and the butter and vanilla extract (make sure it is soft enough to work with).
Rub the butter into the sugar and then bring in the flours until you have a good dough.
Divide this into two pieces and then roll them out on your baking tray into two rounds.
Prick all over with a fork and pinch the edges just to finish them off prettily. Now score into quarters or eighths with a knife but don't cut all the way through.
Bake for about 40 - 45 minutes or until nicely golden.
Sprinkle with caster sugar and cool on a wire rack. Gently break on the score lines to make the traditional triangles.