Dissolve yeast in water. Add flours and leave in a covered bowl for 12 hours.
To make main dough:
Dissolve yeast in water for main dough. Add all remaining ingredients and knead into a dough. Leave dough to rest, lightly oiled in a bowl, covered for an hour. After dough has doubled in size, preheat oven to 230 C (450 F). Shape dough into individual buns weighing 85 g each. Bake for about 20-30 minutes.