In a medium, mix the ingredients for [Sourdough Pre-dough] until no longer floury. Cover with wrap and let proof for 14-18 hours at room temperature. It should be frothy, a little bubbly and have a fragrant sourdough smell (you might have to stir to check).

In a large bowl, mix the [Main Dough] ingredients with the finished [Sourdough Pre-dough] until it forms a workable clump of dough. (if using a standing mixer then just let that do the work)

Knead the dough for 15 minutes until smooth. (if using the mixer, then about 10 minutes). Form into a round ball and put in a large bowl to rise covering with wrap. Let rise at room temperature about 2 hours (after 1 hour, give it an couple of kneads and return to the bowl).

After 2 hours, remove dough from bowl and form into an oval loaf. If you have one, dust a proofing basket (banneton) and surface of bread with potato starch. Place in basket facing down and let rise again for about 45 minutes. If you don't have a proofing basket, just dust the surface of the dough with potato starch and wrap lightly with a tea towel or bread linen, letting rise for 45 minutes.

Meanwhile, preheat the oven to 250°C/480°F along with a steam tray (a shallow pan) at the bottom rack (you'll pour boiling water in later).

When the bread is done rising, place in on a lined baking sheet (unless you have a baking stone, then I'm sure you know what to do). Brush the surface with hot water with a silicon or pasty brush. Cut small slits along both sides of the bread to get the pattern in the photo.

Put bread in middle rack of the 250°C/480°F preheated oven and pour some hot boiling water in the steam pan at the bottom. Bake for 50 minutes. After the first 10 minutes, remove the steam tray and lower the heat to 200°C/400°F and bake for the remaining 40 minutes.

While the bread is baking, prepare the roasted potato starch glaze: Put the potato starch in a small pan on the stove without oil and heat for a few minutes until it turns light brown. Keep an eye on it so it doesn't get burnt. Whisk with 20 ml (4 tsp) water until clumps are gone.

When bread is done, remove from oven to a cooling rack and immediately brush the potato starch glaze over the surface. Let the bread cool for at least 12 hours until slicing to let it develop it's full flavor.