Mix the dry ingredients. Add the flour, sugar, baking powder, and salt to a large bowl. Whisk well to combine.
Add the butter. Add the grated cold butter to the bowl. Using a rubber spatula, gently toss and distribute the butter throughout the flour mixture. Set aside.
Stir the wet ingredients. In a separate mixing bowl, add the egg, sourdough starter, vanilla extract, beaten egg, and heavy cream.
Combine the wet and dry ingredients. Add the wet to the dry, using a silicone spatula to gently stir until a soft dough forms. Do not overmix.
Chill the dough (cold fermentation). Pat the dough into a cohesive disc shape and wrap it tightly in several layers of plastic wrap. Refrigerate (cold ferment) for at least 30 minutes, or overnight (8-12 hours). Fermentation can go as long as 24 hours if desired.
Prepare the oven. Preheat the oven to 425ºF (220ºC) and line a baking sheet with parchment paper; set aside.
Shape the scones. Lightly flour your work surface. Unwrap the chilled dough and place it on the surface. Using a bend scraper or knife, cut the disc in half, then into quarters, and then cut each quarter in half to create 8 scones (wedge-shaped).
Bake the scones. Transfer the scones to the prepared baking sheet, spacing them slightly apart. Brush the tops with heavy cream and sprinkle with raw sugar (if desired).
Bake for 22-25 minutes, or until golden brown with a minimum internal temperature of 200ºF (93ºC)
Serve warm, plain, or with butter and jam!