Ultimate flaky biscuits

Weigh 452 g self-rising flour into a bowl and add 25 g sugar.

Toss the cold butter in the flour to coat, then grate it on the cutting blade of a box grater into thin, long pieces, dredging in flour if it sticks.

Toss the butter pieces to coat and freeze the whole bowl about 15 minutes until dead cold.

Make a well, add 113 g ice water and 113 g sour cream.

Turn the bowl and mix with a flexible scraper, then switch to the hand, pressing and folding to bring the dough together; add ice water half a teaspoon at a time, up to two teaspoons, only if dry flour remains after three or four folds.

Tip out leftover dry flour to use as bench flour and press the dough into a rectangle about 4 by 7 inches.

Check it is not stuck, dust lightly with flour and roll out to 8 by 10 inches, squaring the corners with the scraper.

Brush the surface with a little water so the layers adhere.

Cut in half down the middle and in half again across, and stack the four pieces with cut edges aligned and the last tacky side down.

Clean the bench, dust with flour and press the stack out to 4.5 by 8 inches.

Trim the sidewalls just enough to expose the layers, then cut into eight pieces; bake the scraps too.

Place on a parchment-lined sheet tray and freeze 1 to 2 hours.

Preheat the oven fully to 425F.

Mix 1 tbsp sour cream with 2 tsp water and brush generously on the tops only, not the sides.

Sprinkle a little salt on each top.

Bake in the upper third of the oven 23 to 28 minutes until fully coloured; use a double tray if the oven has strong bottom heat.

Variation: roll the dough a little bigger and cut six for breakfast sandwiches; fill a biscuit with a fried egg, bacon and mango chutney.