Sift the flour into a large bowl and mix with the yeast and sugar.
Melt the butter in a small saucepan, let cool briefly and pour into the bowl. Also stir in the milk and incorporate the egg.
With your hands, or with the dough hooks of a mixer, work into a gelatinous dough and let rise, covered, in a floured bowl for at least 3 hours.
Then divide the dough into three strands and let them rise, covered, for another 30 minutes.
Braid the 3 strands into a plait, lightly press the ends together and brush with the yolk.
Bake the braided bread in a preheated oven at 180 °C for 40-45 minutes, let cool and sprinkle with powdered sugar before serving.