Mix 250g flour with half the yeast pack and 300ml cold water. Leave to rise overnight in the refrigerator, at least 12 hours.
Add the remaining flour (approximately 750g), remaining water (approximately 300ml), 2 teaspoons salt, and remaining yeast to the starter. Process in a food processor for 5 minutes until combined. Transfer to a bowl and let rise in a warm place for 1 hour until roughly doubled.
Preheat oven to 250°C (482°F). Shape the dough into long rolls and cut into 40 equal pieces. Line 2 baking sheets with parchment paper and place the rolls on them. Make shallow cuts across the top of each roll with a knife. Sprinkle with flour or grains and seeds.
Place a bowl of water on the bottom of the oven to create steam. Bake the rolls on the middle rack for 12 minutes until golden.