Start by combining the flour, salt, baking powder and baking soda.
Add the butter and cut it in using a pastry cutter. It must be really cold and cutinto bite-sized or pea size pieces.
Stir in the egg, then add the sourdough starter and buttermilk.
The dough will be sticky. Cover and refrigerate overnight.
In the morning, grab your iron skillet and line with parchment paper.
Preheat the oven to 400 degrees.
Take some flour and spread it out on your counter. Remove the dough from the fridge and grab your rolling pin.
Roll out the dough and take your biscuit cutter and cut them into 1" thick circles.
Place them in the iron skillet or a baking sheet and bake for 15-20 minutes. Once they are golden brown, they are done.