Mix the flour with ¼ teaspoon of sea salt in a bowl, then cube and rub in the lard with your fingers until it resembles breadcrumbs.
Slowly add 100ml of ice-cold water and mix it until you have a smooth dough (add extra water if needs be) – do not overwork. Wrap in clingfilm and chill for 30 minutes.
The butter needs to be cold but soft enough to be malleable. Remove it from the fridge and place it between two sheets of greaseproof paper. Using a rolling pin, roll it out to about 14cm x 16cm.
Remove the dough from the fridge and roll it out on a floured surface to 16cm x 30cm – a little wider than the butter block.
Place the butter on one half, then fold over the other half to cover it, pressing the edges together to seal, and roll back out to 16cm x 30cm. Keep flouring the surface to stop the pastry sticking.
Now fold it into three – fold up one-third from the bottom, then a third from the top over it, using a pastry brush to remove excess flour.
Reseal the edges, turn 90 degrees and repeat the roll and fold. Chill for 20 minutes.
Repeat the rolling and folding process two more times, then chill for 20 minutes. If the butter seeps out while you’re rolling, it’s become too warm, so pop it back in the fridge for 20 minutes – but no longer, as it’ll become too hard.
Remove from the fridge and repeat the rolling and folding two more times, until it’s had six rolls and folds altogether. Chill for a final 20 minutes, then it’s ready.