Pour the milk, egg, sourdough starter and flour in the bowl of a stand mixer.
Knead the ingredients until all the flour is well incorporated with the dough.
Add the butter at room temperature cut in pieces, little by little as you keep mixing the dough, finally add the salt.
Place the dough on your working table, stretch and fold it to add more tension and form a ball.
Place it in a greased bowl and cover it with a plastic wrap or a plastic lid and let it ferment in a warm place until it doubles in size. 4 hours
Take the dough out of the bowl, place it on your working table and stretch and fold it to make a ball of dough again.
Divide the dough in 8 equal pieces.
Shape the dough and make balls of dough.
Place the balls of dough on a prepared baking sheet with parchment paper or a silicone mat and cover the dough with a plastic lid or a plastic wrap and let the dough proof in a warm place for another 2 hours.
Brush the dough with egg wash.
Place the dough in a preheated oven at 375 degrees Fahrenheit for about 30 minutes or until the bread is golden brown.
Take the bread out of the oven and place it on a cooling rack as soon as possible.
