Spread 3 1/2 cups frozen blueberries in an ungreased 8 or 9 inch baking pan.
Sprinkle the blueberries with cornstarch, then drizzle the lemon juice over top. Set aside.
In a medium bowl, combine the flour,1/2 cup of turbinado or regular sugar,baking powder and salt. Stir to combine. Add the milk and butter. Stir till just combined. Dough will be lumpy, not smooth.
Drop mounds of dough on top of the blueberries, I was able to get 9 nice mounds.
Pour the boiling water over dough and blueberries. Sprinkle the remaining 1/4 cup sugar over the dough and blueberries. Bake at 350 degrees until biscuits are golden brown and blueberries are bubbly, 45 - 50 minutes. It took 50 minutes in my oven. Serve warm or room temperature with vanilla ice cream.