In a 10-inch cast iron or ovenproof skillet, combine blueberries, 1/2 cup granulated sugar, corn starch, lemon zest, lemon juice, nutmeg and salt in a 10-inch. Bring to a boil and then simmer for 10 minutes or until the berries begin to break down and the mixture slightly thickens. Remove from heat and set aside.
In a medium bowl whisk flour, baking powder, baking soda, and salt. Set aside. In a small bowl, whisk buttermilk, melted butter, and vanilla extract. Add wet ingredients to dry and stir until just combined - do not overmix. Scoop dough by heaping tablespoon; flatten each spoonful and place the "biscuit" carefully on top of the hot berry mixture, about 1-inch apart. In a small bowl, combine two teaspoons of granulated sugar with the cinnamon and then sprinkle evenly, generously coating each biscuit.
Bake in a 400°F oven for 15 to 18 minutes or until bubbling and the biscuits are golden brown on top and cooked through. If your skillet is very full, you may wish to place a baking sheet on a rack below your skillet to catch drips. Remove from oven and cool for 10 minutes or until ready to serve. Serve with vanilla ice cream if desired. Leftovers can be kept in an airtight container in the refrigerator for up to two days. This dessert is best the day it’s made, but it makes a great breakfast the next day, too.
Note: if you do not have an ovenproof skillet, you can use a 9x9-inch or 10-inch round baking pan; simply cook fruit in a skillet or saucepan then transfer to baking pan, then proceed to add 'biscuits' and bake as directed.