In a large bowl, whisk the egg. Reserve 1 tablespoon in a separate bowl.
To the remaining egg, whisk in the sugar and yeast.
Add the bread flour and salt.
Add the warm milk.
Stir with a wooden spoon until in it forms a shaggy dough.
Turn the dough out on to the counter and knead 1 minute to form a ball.
Cover the dough with a damp towel and let it rest for 10 minutes.
Knead for 5 minutes or until the surface of the dough is smooth.
Press the dough out and add the butter. Pull the dough up and around the dough and knead until fully incorporated. It will initially look like a mess, but it will eventually get absorbed into the dough.
Form the dough into a ball and place on a parchment lined baking pan.
Cover with a damp cloth and allow to rise in a warm room or in a proofer set to 86˚F/30˚C 1 hour or until doubled in size.