Mix the sourdough pre-dough together in a small bowl. Cover and let rest for 12 hours at room temperature.

After 12 hours, mix the pre-dough with the main dough ingredients in a large bowl until the dough comes together.

Remove to a floured working surface and knead for 15 minutes until smooth and elastic.

Fold in the chocolate in batches.

When all chocolate is folded in, knead for 1 more minute.

Return dough to bowl, cover and let rise 2 hours at room temperature.

After 2 hours, divide the dough into two equal portions. Shape into a round boules or longer oval loaf, or one each.

Dust with a little flour and cover with a clean cloth. Let rise another 3 hours.

Cut a slit down the center of each bread dough right before putting in oven to bake.

Pour in some boiling water into the tray, then immediately put in the bread. Bake at 230°C/445°F for 10 minutes then remove the steam tray. Lower heat to 190°C/375°F and bak for another 25 minutes. (Total 35 minutes). Remove and let cool on a rack.