Mix the flour and sugar first, and then rub in the butter.
Knead the mixture until it becomes a smooth paste.
Roll out till about 3/4 inch (2 cm) thick.
Cut into rectangles and decorate the top with a fork creating rows of holes.
Transfer to a greased baking sheet and bake for 20-25 minutes at 160C (325F/Gas Mark 3). They want to stay pale and light golden.
In warm weather you may want to chill the cookies before baking.
To use a shortbread mold: Mix a teaspoon of flour and a teaspoon of caster sugar. Grease the mold with oil and evenly sprinkle half the flour/sugar mix. Press the shortbread into the mold, and turn out onto a baking sheet before baking.