Mix yeast with milk, flour, salt and sugar. Knead the dough for 5 minutes on low speed, then switch to medium speed and knead for 12 minutes until the gluten develops.
Beat the butter with a rolling pin to make it plastic. Add the butter in pieces and knead for another 5 minutes. Leave the dough for 1 hour.
Divide the dough into portions of 150 g, roll up and leave under the film for 15 minutes. Shape into batards or round buns.
Leave the buns on the baking sheet for 2 hours. Then make cuts on each bun and brush with an egg mixed with 1 tsp. water.
Bake the buns in the oven for 40 minutes at 220°C.