Sprinkle yeast over the water. Leave for 5 min. Stir to dissolve.

Mix flour and salt together in a large bowl and make a well in the centre

Pour sourdough start into the well in the flour mixture.

Pour over the yeasted water.

Mix in the flour from the sides to form a stiff, sticky dough. (If the mixture is too dry then add up to 1 tablespoon of water - 1 tablespoon is a lot.)

Turn the dough onto a lightly floured work surface. Knead until smooth and elastic (about 10 min)

Put the dough in a lightly oiled bowl, cover and leave to rise for 2 hours.

Knock back. Leave to rest for 10 min.

Shape the dough into a round loaf.

Place on a floured baking sheet, cover, and prove until doubled in size (about 1 hour; the book says 1 1/2 hours but I found this too long and the dough becomes over-proved.)

Dust the loaf with flour.

Cut slashes in the top (a grid formed by 3 parallel slashes crossed by another set of 3 is traditional)

Bake at 220º C until golden brown and hollow sounding (about 30-40 min; the book says 60 min, but I've never had to cook for longer than 40 min).

Leave to cool on a wire rack.