This is another dough that went through its adolescence with yeast, then grew up into an honest sourdough (see for the recipe for potato bread junior). We use desiree potatoes as they are consistently good all year round, but you can use any potato really. The potatoes are first tossed in olive oil, then seasoned and roasted in a hot oven to partially cook them before adding to the dough. Nigella seeds are also called kalonji at the Indian grocer and are often mistakenly called black or cumin seeds.