Preheat oven to 450°F. While the oven is heating, put the oil into a 10-inch cast-iron skillet and place in the oven while the oven preheats.
Meanwhile, mix together the cornmeal, flour, sugar, baking powder, baking soda, lime zest, nutmeg, and salt. Whisk together the egg and buttermilk and pour into the dry ingredients. Stir until well combined.
Take the cast iron skillet out of then oven, and pour the hot oil into batter and stir until well combined. Add the blueberries and gently stir until evenly distributed.
Pour the batter back into the hot skillet and bake for 18-20 minutes or until the top is lightly browned and an inserted knifes comes out clean. Serve warm.