Add the flour, cocoa powder, espresso powder, sugar, baking powder, chocolate chips, and salt to a large bowl. Whisk together.
Add the sourdough starter, egg, heavy cream and vanilla to a separate smaller bowl. Whisk thoroughly.
Grate frozen butter into the dry ingredients. Gently fold the butter into the dry ingredients, just enough to coat the butter in the flour mixture. (See notes below on how to use a food processor instead of a grater.)
Pour the wet ingredients into the dry ingredients and gently mix. It will be thick and dry. The key to this recipe is to NOT over-mix. You want the grated butter to stay in small pieces and NOT be totally mixed into the dough. This is how the scones stay flaky.
Once you’ve given the dough a gentle initial mix, dump it onto a work surface. Use a bench scraper to continue cutting the mixture together, then use your hands to shape the dough into a round disk (Roughly 1.5" thick). Again, be careful to not overwork the dough. You don’t want the warmth of your hands to melt the butter into the dough!
At this point, you can move straight into baking, refrigerate for a few days, or freeze the dough. If you refrigerate or freeze, wrap the dough tightly in plastic wrap. Although optional, letting the dough get nice and cold before baking makes them even better!
Preheat the oven to 400°F. Cut the scone disc into 8 even triangles (like a pizza).
Brush heavy cream on top of each scone and sprinkle with sugar before baking.
Bake for 15-18 minutes, until the scones are fully set.
Optionally, drizzle melted chocolate over the scones once cooled for an extra burst of chocolate