230g plain flour
110g golden caster sugar
230g cold butter, diced
100g chocolate of your choice, cut into small chunks.
Preheat the oven to 160*C/325*F, and butter a 25cm tart tin.
Sift the flour and cornflour into a bowl, and mix in the sugar. Start to add butter and mix it together with your fingers, rubbing it in gently with fingertips.
Bake in the heated oven for around 40 minutes. It should be a pale golden colour but not brown. Mark out how many slices you want and let cool slightly in the tin before transferring to a wire rack.