Crumble the yeast with a tablespoon of sugar in a large cup, cover with a little lukewarm milk and let rise until the cup is full of swollen yeast.
In the meantime, put the flour in a bowl, make a large depression in the middle, add the salt and sugar on the outside.
Dissolve the butter in a saucepan, do not let it get hot.
Pour the swollen yeast into the well, add the butter vanilla flavor and the rest of the lukewarm milk. Add the dissolved, not hot butter and stir everything. Let rise for 15 min. Knead the dough well and let rise for another 45 minutes. Knead the dough vigorously one more time and let rise for another 30 minutes
Put the dough in a large loaf tin (35 cm) lined with baking paper and cut into it lengthways. Brush with beaten egg and bake for 45 minutes at 190-200ºC.