Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper or a silicone baking mat to prevent the scones from sticking and to ensure even browning.
In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, cocoa powder, baking powder, and salt until well combined and there are no large lumps of cocoa.
Add the cold, cubed butter to the flour mixture. Using a pastry cutter or two forks, work the butter into the dry ingredients until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining. Stir in the chocolate chips.
In a separate small bowl, whisk together the heavy cream, egg, and vanilla extract until smooth.
Pour the liquid mixture into the dry ingredients. Stir gently with a spatula just until the dough starts to come together. Do not overmix; the dough should look a bit shaggy.
Turn the dough onto a lightly floured surface. Gently knead it 3 or 4 times just to bring it together into a ball. Pat the dough into an 8-inch disc about 1 inch thick. Use a sharp knife or a bench scraper to cut the disc into 8 equal wedges.
Place the wedges onto the prepared baking sheet. Brush the tops with a little extra heavy cream and sprinkle with coarse sugar if desired. Bake for 15 to 18 minutes, or until the edges are firm and the tops look set. Let them cool on the pan for 5 minutes before transferring to a wire rack.