Preheat the oven to 375 degrees F. Line a baking sheet with parchment paper.
Whisk together the flour, cocoa powder, granulated sugar, espresso powder, baking powder and salt. Add the cold cubed butter and use a pastry blender or your fingertips to blend the butter into the dry ingredients until the mixture looks like damp sand with some larger pea-sized pieces of butter throughout.
Make a well in the center of the flour and butter mixture. Reserve 1 tablespoon of the chopped espresso beans, if using, for garnish and sprinkle the remainder around the edge of the flour well. In a small bowl, whisk together the cream, egg and vanilla. Pour the liquid ingredients into the well in the center of the flour mixture. Pour in the melted chocolate. Stir just until all the ingredients are moistened and dough begins to come together; it's okay if the mixture has some light and dark streaks. Turn the dough out onto a lightly floured work surface and gently pat it together into a round about 7 inches in diameter and 3/4 inch thick. Using a sharp knife, cut the dough into 8 equal triangular slices. Sprinkle turbinado sugar over the top of the dough and press gently to adhere.
Transfer the scones to the prepared baking sheet. Bake until the scones are slightly firm to the touch and a toothpick inserted into one comes out clean (a few small crumbs clinging to the toothpick are okay), 15 to 20 minutes. Transfer the scones to a wire rack to cool completely.
Meanwhile, for serving, beat the mascarpone, granulated sugar and heavy cream with an electric mixer on high speed until soft peaks form. Serve the scones with a dollop of the mascarpone cream and a sprinkle of reserved espresso beans.