In the bowl of a stand mixer fitted with the dough hook, combine the sourdough starter, lukewarm water, egg, cooled melted butter and sugar. Turn the mixer onto a low speed and stir until roughly mixed together.
Add the flour, salt and (if using) the easy-bake yeast (see notes below for if you are using it). Turn the mixer onto a medium-low speed until the dry ingredients have been mostly mixed in then increase the speed to high. Let it knead the dough for 6-8 minutes until it is smooth, elastic and is pulling way from the sides of the bowl.
Pour a little bit of vegetable oil over the dough and turn it to coat the dough and bowl with a thin layer of oil.
Cover with a clean tea towel and leave somewhere warm for around 4 hours - during this rising time you need to turn the dough. This is done by grabbing the 'north' side of the dough, pulling it up and folding it down towards the opposite side of the dough. Then repeating this in the same manner with the 'east', 'south' and 'west' sides of the dough. This is one set of turns. You need to do 4 sets of turns throughout the rising time, so once per hour is about right.
Once you've completed your last turn of the dough, let it rest somewhere warm again so it becomes puffy - about 30-45 minutes.