Combine the flour, sugar, cocoa, baking powder, and salt in a large bowl. Add the butter and cut it in with a pastry blender or fork until the mixture is rough and crumbly.
Add the 1 cup of heavy whipping cream, melted chocolate, and vanilla. Stir with a fork just until the dry ingredients are moistened. Knead the dough lightly 3 or 4 times in the bowl.
Lightly coat a baking sheet with cooking spray. Turn the dough out onto the baking sheet and pat it into an approximately 8-inch circle.
Using a sharp knife, cut or mark the dough into 8 wedges. Don’t separate the wedges. Brush with the remaining whipping cream or milk and sprinkle with turbinado or granulated sugar.
Bake for 19-20 minutes or until done. Be careful not to overbake.
Best served warm with a dollop of whipped cream.
Notes
This is a very moist, almost wet, dough. If you can't cut it before baking, just cut it when it comes out of the oven.