A few notes: I made this twice in a 9x13-inch pan, and I didn't think there was enough topping. 6 cups of blueberries, however, definitely is enough for a 9x13-inch pan, so if you like that vessel, I suggest doubling the topping recipe (without doubling the quantities of baking powder and baking soda). I happen to have a deep 9-inch pie plate, but otherwise, I think 6 cups of blueberries would have been too much for my other, more shallow pie plates. (Doubling the topping for a 9-inch pie plate, by the way, is not a good idea...tried that.) I also made a few other small changes: I omitted cinnamon from both the filling and the topping. I omitted the 2 tablespoons of cornmeal, which I liked initially, but prefer without — I just prefer the flavor of a pure buttermilk biscuit without a hint of cornbread. The original recipe also calls for melting the butter, but I find using cool butter actually easier than melting butter. But by all means, melt the butter. Finally, I used turbinado sugar for sprinkling and brushed the biscuits with milk before sprinkling with sugar — it's just what I've always done with this recipe. If you want to follow Cook's Illustrated recipe exactly, follow this recipe.