Add the butter and continue to whisk while adding the remaining flour. Turn the dough over on a floured surface and knead it a few times. Place the dough in an oiled bowl and cover it with a clean towel. Let it sit and double in size, anywhere from 1 to 2 hours, in a warm place.
After 10 minutes, add the egg and milk and whisk. Add the salt and add half the flour and whisk well until everything is well incorporated.
In a big bowl, add the water, sugar and yeast. Whisk it all together and let it sit for about 10 minutes.