Preheat oven to 425 degrees. Make sure the oven rack is in the center of the oven. Line a sheet pan with parchment paper and set aside.
Whisk the flour (1 ½ cup), granulated sugar (¼ cup), and baking powder (4 tsp) together in a medium mixing bowl. Toss the butter (6 tbsp cut into ½ in cubes) into the mixture, coating it. Using a pastry cutter or your hands, work the butter into the flour until the mix is mealy and small pea size pieces of butter remain.
Add the blueberries (¼ cup) and toss. Make a well in the center of the mix and add 4 tbsp of heavy cream and ¼ cup water. Toss with a fork until the dough is evenly damp and shaggy. DO NOT OVERWORK THE DOUGH.
Add 1 to 3 tsp more water if the dough is too dry.
Drop 6 mounds (roughly ⅓ cup each) onto the baking sheet and gently press them down. If there are bits of stray dough, gently press them into the mound.
Lightly brush the tops of the dough mounds with heavy cream (roughly 2 tbsp will be used).
Bake for 15 minutes, until the tops are golden brown and the biscuits are cooked through. Remove from the oven and sprinkle sugar over the tops. Transfer to a wire rack to cool for 5 minutes.
