For the biscuits: Heat the oven to 500 degrees F. Spray an 8-inch round cake pan with nonstick spray and set aside. In a bowl, combine 2 cups of the flour, the baking powder and salt. Using a pastry cutter or 2 knives, cut the butter into the flour mixture until it resembles coarse meal. Pour in the buttermilk and gently mix until just combined; use enough buttermilk so that the dough is very wet and looks like cottage cheese.
Place the remaining 1 cup flour in a shallow bowl. Spray a medium ice-cream scoop or tablespoon with nonstick spray. Scoop up some biscuit dough and drop it into the flour. Sprinkle flour over the top and roll the dough gently in the flour. Shake off excess flour and shape the dough into a round. Place it in the prepared cake pan. Continue process until all the dough is used, making 8 to 10 biscuits and pressing them snugly next to each other in the pan. (This will keep them soft and tender.) Bake until golden brown, 12 to 15 minutes. Transfer the pan to a rack to cool just slightly. Serve warm.
For the chocolate gravy: Meanwhile, in a medium heavy saucepan, whisk together the sugar, flour and cocoa until no clumps of flour or cocoa remain. Whisk in the milk until well combined. Place over medium heat and cook, whisking constantly, until the mixture begins to boil and then thickens like gravy, 5 to 10 minutes. Remove the saucepan from the heat and stir in the butter until it melts. Spoon warm gravy over the warm biscuits and serve the remaining gravy on the side.