Crumble the yeast into 300ml warm water and add the sugar. Stir and leave in a warm place for 5-10 minutes, until foaming. Mix the flours and salt and make a well in the centre. Pour in the yeast liquid and mix, gradually adding enough water to form a soft but not sticky dough. Knead vigorously for 10 minutes, until smooth and elastic. Return to the bowl, sprinkle with a little extra flour and cover with a cloth. Leave at room temperature for 2-3 hours, until doubled in bulk.

Punch down and knead again for 5 minutes. Shape into a large round loaf and place on a greased baking tray. Leave to rise again, dusted with flour and covered with a cloth for a further 30 minutes or so.

Preheat the oven to 220c/425f gas 7. Make criss-cross slashes across the surface of the dough, then bake for 35-45 minutes, until cooked. Test by tapping the underneath - if it sounds hollow, the loaf is done. Cool on a wire rack.