Preheat oven to 375 degrees. Pulse flour, baking powder, and salt in a food processor until combined. Add butter, and process until mixture resembles coarse meal. Transfer mixture to a large bowl, and add heavy cream in a slow, steady stream, mixing with a wooden spoon until dough just comes together. Divide dough into 9 pieces, and loosely form each into a ball and flatten slightly. Set aside.
In a medium bowl, combine blueberries, sugar, cornstarch, and cinnamon; toss gently to coat. Transfer mixture to an 8-inch square baking dish. Top blueberry mixture with dough balls, spacing evenly. Brush dough with heavy cream, and sprinkle with sanding sugar. Bake until berries are bubbling in center and biscuits are golden brown, about 55 minutes. Transfer dish to a wire rack, and let cool slightly, about 30 minutes.