Preheat the oven to 400 degrees F.
Lightly grease, a large cast iron skillet, and set aside. You can also use a glass baking dish or a Dutch oven. If you like you can line your pan with parchment paper, but I've never had my bread stick to the pan.
In a small bowl whisk together the wet ingredients(the buttermilk, egg, and sourdough discard) and set aside.
In a large bowl, combine the dry ingredients (the flour, sugar, baking soda, and sea salt.) Add the cubed butter and mix with your hands or a pastry cutter, until it resembles coarse, pea-sized crumbs.
Pour the milk mixture, into the flour mixture, and using a dough whisk or your hands, mix the dough just until it comes together.
Turn the dough out onto a lightly floured surface, and gently knead until the dough comes together enough for you to form a ball. Your dough should be slightly wet and resemble biscuit dough.
Shape your dough into a ball, and place it in your prepared skillet.
With a sharp knife, cut a slit in the top of the bread, roughly 4 inches long and 1/2 inch deep. You can also cut a deep cross on the top of the dough.
Place the bread in the preheated oven and bake for 45-55 minutes, or until the bread is golden brown and cook through. (see notes if you are having trouble baking your bread)
Remove the bread from the oven and allow it to cool, either in the skillet or on a wire rack for 10 minutes before serving.
Enjoy!