Adapted from Dan Lepard: The Handmade Loaf (Mitchell Beazley Food)
- Whisk the leaven with water, honey and grated potato in a large bowl. Combine the flours and salt. Mix the ingredients together to form a sticky mass. Cover with a cling film and leave for 10 minutes. Spread a teaspoon of olive oil on the work surface. Scrape the dough, working from the side of the bowl, on to the oiled surface. Knead briefly, 20 seconds, will be enough. Clean the bowl, and give it a light rub with olive oil. Return the dough to the greased mixing bowl. Cover and leave overnight in fridge.
- Scrape the dough on to a lightly oiled work surface and pat it out to form a rectangle, roughly 40cm x 20cm. Fold one end, a third of the length, back to the center. Fold the other end back over it, so you have three layers. Pat it out again and fold it once more. This stretches the dough and aerates it. Leave one hour at room temperature and repeat. Leave another hour and repeat. The dough should be rising nicely. The most important thing to remember is that it's ready to shape when bubbles form in the dough. To check, slash the dough with a sharp razor. If this hasn't happened, leave the dough a further hour and check again.
- Shape the dough into a ball. Cover and rest for 15 minutes. Dust a parchment paper or a towel and lay it on a tray. Use a flour-dusted, linen-lined basket if you have one. Shape the dough into a baton and place it seam-side up on the prepared paper or cloth. Cover and leave at room temperature until almost doubled, about 3-4 hours.
- Preheat the oven to 220C425F. Turn the loaves on a floured baking sheet, so that any seams are now underneath. Make a cut a along the loaf’s length. Bake for 25 minutes. Reduce the heat to 180C350F and bake for 45-55 minutes. Remove from oven and cool on a wire rack.