For bagels with poppy seeds, first bring the milk briefly to the boil and remove from the hot stove. Add butter and sugar and let it melt. When the milk is lukewarm, stir in dry yeast and let stand for ten minutes with the lid closed.
Beat in egg whites, salt and flour and combine to form a soft dough. Cover and let rise at room temperature until doubled in volume.
Divide dough into portions and shape into rings. Let rise on a floured parchment paper.
Then dip one bagel at a time into lightly simmering water for 15 seconds. Transfer to a baking sheet lined with parchment paper, brush with egg yolk and sprinkle with poppy seeds.
Bake the bagels with poppy seeds in the middle of the oven heated to 200 °C for twenty minutes.