Heat the oven to 160°C conventional, 140°C fan or gas mark 3. Grease and line a 20 cm square tin, or prepare a baking tray if you plan to roll and cut the dough.

Cream the softened butter and caster sugar lightly until smooth. Mix only until combined and creamy, because excessive whipping adds air and makes the shortbread less traditionally dense.

Add the plain flour and optional pinch of salt to the butter mixture. Stir gently until a soft dough forms, stopping as soon as there are no obvious dry patches.

Press the dough evenly into the prepared tin, or roll it to approximately 1 cm thickness and cut it into fingers or rounds. Aim for an even thickness so every piece bakes at the same rate.

Prick the surface all over with a fork. These small holes are characteristic of shortbread and help prevent large air pockets while the dough bakes.

Chill the shaped dough for 20–30 minutes if time allows. This firms the butter, helps the shortbread hold its shape and reduces spreading in the oven.

Bake for approximately 20–30 minutes, checking toward the shorter end of the cooking time. The shortbread should feel firm and remain pale, with only very lightly golden edges.

Sprinkle the hot shortbread with extra caster sugar as soon as it comes from the oven. Cool it in the tin for 10–15 minutes, then transfer it to a rack and allow it to cool for at least 15 minutes before serving.