Preheat the oven to 425°F and grease a 3 quart casserole dish with vegetable shortening. Set aside. You can use a smaller or large casserole dish, but this will also impact baking time.
In a large mixing bowl, whisk together the flour, cornstarch, baking powder, baking soda, brown sugar and salt.
Using a pastry cutter, blend in the cold butter.
Stir in the buttermilk until a coarse and lumpy batter forms. Scoop this into the prepared baking pan, set aside. They will spread, this is normal.
In a medium mixing bowl, stir together the sugar, cinnamon and nutmeg.
Baste the tops of the biscuits with heavy cream (or buttermilk) and top with the cinnamon sugar mixture. Using a knife or large toothpick, swirl the topping around.
Bake, uncovered for 25-27 minutes or until the tops are lightly browned and it passes the toothpick test.
Remove and allow to cool before cutting with a serrated knife.
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Notes
To take this up a notch, consider drizzling with powdered sugar icing!