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Shortbread (Butter, Sugar, Flour and No Added Water)

Name: Shortbread (Butter, Sugar, Flour and No Added Water)
Prep time: 45 min
Cook time: 55 min
Total time: 1 h 40 min
Yield: 8 servings
Cuisine: British
Ingredients: 100 g unsalted butter; 50 g caster sugar; 120 g plain flour; 30 g rice flour; 1 pinch salt; 1 tbsp caster sugar

The Scottish biscuit that is short in the baker's sense. Gluten needs water to form, and none is added beyond the little inside the butter, so there is no gluten, no flake and no layers, and it crumbles. Butter set hard again holds it together, so it is cut hot and left to cool in the tin.

Ingredients

8servings

The dough (one 20cm square tin, 12 pieces)
unsalted butter · cool room temperature, 18-20°C. Soft butter spreads100 g
caster sugar50 g
plain flour120 g
rice flour · gives the sandy break. Cornflour or fine semolina stand in30 g
salt1 pinch
To finish
caster sugar · scattered on straight out of the oven1 tbsp

Steps

Beat the butter and sugar for two minutes only. Do not take it pale and fluffy. Pound cake creams butter to get air in, but there is no added liquid and no leavening here to hold that air. All you are doing is spreading the butter evenly through the sugar.
⏲ 2 min
Sift in the plain flour, rice flour and salt and bring it together with a spatula or your hands only until it clumps in your fist. Do not knead it — strictly, there is nothing to knead. Gluten needs water to form and none is added to this dough, so working it longer builds no gluten and instead melts the butter with the heat of your hands (dough and gluten, choosing flour).
⏲ 3 min
Tip it into a lined 20cm square tin and press it out flat, about 1cm thick, with your hands or the base of a cup. Do not roll it.
⏲ 5 min
Prick it all over with a fork. Not decoration — the reason mille-feuille gives: with no way out, the steam that forms inside lifts whatever spot is weakest. Then score the twelve pieces now, before it goes in.
⏲ 2 min
Chill 30 minutes to set the butter hard again. A soft dough spreads in the oven and comes out thin at the edges.
⏲ 30 min
150°C for 45-55 minutes. Low and long. The aim is to dry it out rather than brown it, and a dough over 30% butter put into a 180°C oven burns its milk solids first (browning and Maillard, what your oven is doing). Done, it is pale straw, not golden.
⏲ 50 min
The moment it comes out, cut along the lines you scored and scatter the sugar over. It is still soft now, so the knife goes straight through. Cut cold it shatters.
⏲ 2 min
Cool it completely in the tin. Straight from the oven shortbread collapses if you lift it. What makes it firm is the butter setting again, and that is the whole of its structure. It keeps two weeks in a tin.

Variations

Without rice flour: 150g of plain flour works. It comes out slightly denser and less sandy. Semolina gives a coarser break again.
Millionaire's shortbread: this dough as a base under caramel and chocolate, which brings with it the whole chocolate-lid problem nanaimo bars explain.
Other flavours: lemon zest, lavender, rosemary, caraway. In Scotland it is never missing at Christmas and Hogmanay.

More detail and the reasons why (4)

The exact opposite of biscotti. That page says "the absence of fat is not an omission; it is the condition for keeping" — no butter, no oil, no milk, egg standing in for the liquid, and the result snaps. Shortbread is fat at its maximum and no added water, and the result crumbles. Both keep for weeks, for opposite reasons.
Against scones and samosa: all three put fat into flour. A scone takes milk, so it has water, and cold flakes of butter give it a flaky lift. A samosa is bound stiff with water and its fat makes layers that shatter in the fryer. Shortbread has no added water, so it has no layers at all. What separates the three is not the fat-to-flour ratio but whether there is any water.
1 : 2 : 3 is the recipe: one sugar, two butter, three to four flour. ko.wikipedia sets it out in exactly those terms. Cut the butter and you have a different biscuit; raise the sugar and it spreads.
The shape is the name: fingers cut into bars, petticoat tails cut as wedges from a round, and thick rounds stamped in a wooden mould. The photograph has fingers and petticoat tails together.

Tips

Do not judge it by colour. If it has browned you are already past it. Look at 45 minutes and stop when the faintest gold shows at the edges.
No dusting flour. There is nothing to roll, so there is nothing to dust, and added flour throws the ratio out.
Do not skip the fork holes. Without them the middle domes up and the thickness stops being even.

More detail and the reasons why (2)

Soft butter is how this fails. Cool room temperature is the target: a fingertip leaves a mark but does not sink in. Too soft and you have made a cream rather than a dough, and it spreads in the oven.
Cut hot, cool in the tin. Do it the other way round and you have crumbs instead of pieces. Where chiffon cake stays soft cold because its fat is oil, this one goes firm precisely because its fat is butter.