Mini burgers with herring, avocado, beetroot and mustard foam

Ingredients for mini rolls:
25 g fresh yeast
250 ml warm milk
1 teaspoon sugar
500 g wheat flour
5 yolks
1 egg
1 teaspoon salt
80 g butter
* All ingredients for the rolls should be at room temperature!
Additionally:
egg yolk with one tablespoon of milk for brushing the rolls
sesame seeds
Ingredients for burgers:
1 jar marinated herring 400 g SEKO
1 avocado
1 roast beetroot
1 red onion
rocket
lemon juice
chilli flakes
salt
black pepper
brine from 200 g tin of chickpeas
1 tablespoon whole grain mustard

Rolls:
Break the yeast into a cup, add 1 teaspoon of sugar and 1 tablespoon of flour. Add warm milk and mix thoroughly. Leave in a warm place for about 10-15 minutes to rise.
Sift the flour into a bowl and make a depression. Pour in the activated yeast, egg, yolks and mix everything with a wooden spoon. Add salt and mix for a little while longer. Knead by hand or with a stand mixer for about 5 minutes. The dough will be sticky, but do not add flour.
Then add soft butter in batches, kneading all the time. Knead for about 15 minutes until a smooth and elastic dough is formed.
Cover with a cloth and set aside in a warm place to rise for about 1 and 1/2 hour.
After this time, knead the dough manually for a while and then, tear off small pieces of dough (about 50 g) and form small rolls. There should be approx. 18 of them.
Place the rolls on a baking tray lined with parchment paper, leaving large gaps between them. Gently flatten each roll with your hand and let rise again for about 30 minutes.