Mix together the yeast, sugar and water and leave to stand for 15 minutes, covered. Heat the buttermilk and melt the butter in it. In a large bowl, knead all the ingredients in the food processor (dough hook) for 5 minutes on a low level to form a smooth dough. Cover and let rise in a warm place for 30 minutes until the volume has visibly increased. Knead again vigorously by hand and shape into 12 balls of 65 g each (the rolls will still open while brewing).
Bring a large pot half full with water to the boil, turn the heat down a little and scald the pieces of dough in portions for 2 minutes on each side. Lift out with a slotted spoon and drain well on kitchen paper.
Make a cut with a sharp knife and, possibly sprinkled with the seeds, place on a baking sheet lined with baking paper. Bake in the preheated oven at O / U 220 ° in the upper area for 15-18 minutes until golden brown.