In a large bowl, whisk the flour, cocoa, sugar, baking powder, cinnamon, and salt. Grate the frozen butter (I used a box grater; a food processor also works - here is the one I own and love). Toss the grated butter into the flour mixture and combine it with a pastry cutter, your fingers, or two knives until the mixture resembles coarse meal. Set aside.
In a small bowl, whisk the cream, egg, and vanilla together. Drizzle it over the flour mixture and then toss the mixture together with a rubber spatula until everything appears moistened. Add more heavy cream, 1 teaspoon at a time, until it comes together, if needed. Slowly and gently fold in the chopped chocolate. Try your best to not overwork the dough at any point. Work the dough into a ball with floured hands (I flour mine with a mix of cocoa powder and flour) as best you can and transfer to the prepared baking sheet. Press into a neat 8″ disc and cut into 8 equal wedges with a very sharp knife. Separate the scones and line them on the baking sheet with a little space between each one.
Bake for 20-25 minutes or until cooked through; use a toothpick to check for doneness--a toothpick inserted will come out mostly clean. Remove scones from the oven and allow to cool for just a couple minutes. During this time (or while the scones are baking) prepare the glaze by whisking the confectioners' sugar, vanilla, and water together until smooth and thin. Dunk warm scones into the water and place on a wire rack with a baking sheet or paper towels underneath to catch the glaze as it drips down. The glaze will set after several minutes, but you can serve right away. Before serving, melt the 4 ounces of semi-sweet chocolate in the microwave in 15 second increments, stirring after each increment until melted. Drizzle over scones.
GLAZE + TOPPING: