Mix 200 g/7 oz of the flour with all the yeast and enough warm water to make a thick batter, then leave to rise overnight.

Add the rest of the flour, the salt and butter to the dough and slowly add enough water to make a soft, pliable dough.

Rest the dough for 1 hour.

Line a baking tray.

Bang the air out of the dough and roll into a baguette shape.

Put it on the baking tray and leave to prove for 1 hour.

Preheat the oven to 220°C/425°F/gas mark 7.

Before the dough goes into the oven, using a sharp knife, make slashes along its length.

Bake for 30 minutes, then transfer to a wire rack to cool.