Prepare the sheet pan. Preheat oven to 375°F / 190*C. Line a baking sheet with parchment paper.
Prepare dough. In a large bowl, sift together 2 cups flour, ½ cup sugar, ¼ cup cocoa powder, 1 Tbsp baking powder, and ½ tsp salt. Add 8 Tbsp grated butter, then stir to evenly coat.
Combine wet and fry ingredients. In a small bowl, whisk together ½ cup heavy cream, 1 egg, and 1 tsp vanilla extract. Pour into flour mixture and stir until a dough begins to form (it will be very crumbly and look dry). Knead with your hands for about 1 minute until the dough becomes a little more smooth. Add chocolate chunks and knead until combined and the liquid has been absorbed into the flour.
Roll out the dough. Gently press or roll dough out into a 6 x 10-inch rectangle. Using a knife or pastry cutter, cut the dough once horizontally and once vertically to create 4 equal rectangles. Make 2 more vertical cuts (one on each side of the center) to create 8 equal squares. Cut each square into 2 triangles — you should have 16 equal wedges.
Chill before baking. Transfer scones to baking sheet leaving about 1 inch in between. Refrigerate formed scones for 15 minutes or place in a freezer for 5 minutes. You want the butter and scone dough as COLD as possible. Just before baking, brush a small bit of reserved heavy creamy on top of each scone.
Bake. Bake for 15 minutes, or until a toothpick placed in the center of the scone comes out clean. Be careful not to over bake! Scones will firm up as they sit. Let scones cool for about 5 minutes, then transfer to a wire rack to cool completely.
Make the icing. While scones are cooling, make icing. Place 1 cup confectioner’s sugar and 1 tsp vanilla in a small bowl, then milk 1 tablespoon at a time, whisking to combine, until desired consistency is reached. Less is more — the less liquid you use, the better the icing will firm up once it sets.