Place a rack in the middle of the oven and preheat it to 400ºF (200ºC). Line a baking sheet with parchment paper and set aside.
Whisk together the flour, sugar, baking powder, and salt in a large mixing bowl.
2 ¼ cups all-purpose flour, ½ cup granulated sugar, 1 tablespoon baking powder, ½ teaspoon salt
Add the butter to the bowl. Quickly break up any large chunks with a pastry blender or your hands. The butter mixture should be coarse and crumbly and the butter should be about the size of green peas.
½ cup salted butter
Stir in the chocolate chunks, then make a well in the middle of the flour. Add the buttermilk and sourdough starter. Use a fork to whisk the buttermilk and starter together, then start incorporating the flour. Once the dough is rough and shaggy and mostly sticking together, quickly gather it into a ball with your hands, making sure to incorporate any dry bits of flour in the bottom of the bowl.
1 cup chocolate chunks, 1 ¼ cups buttermilk, ½ cup sourdough starter
Sprinkle a bit of flour on a work surface. Dump the dough out. Use your hands to quickly and gently press it into a circle about 8 inches (20 cm) in diameter and 1 inch (2 ½ cm) thick. Use a sharp knife to slice the dough into eight wedges. Transfer the wedges to the prepared baking sheet, leaving some space between each.
Brush the top of each scone with buttermilk and sprinkle with coarse sugar if using. Place the tray in the preheated oven and bake the scones for 20 to minutes or until pale gold on top. Transfer the tray to a wire rack and cool the scones for 15 minutes before serving.
Coarse sugar
Notes
If your butter isn't cold, place the mixing bowl in the freezer for 30 minutes after mixing it into the flour then proceed with the recipe as written.