Preheat the oven to 350ºF (177ºC). Grease an 8-inch cast iron skillet.*
Set aside 1/4 cup of blueberries. In a small bowl, toss the remaining 1 cup of blueberries with 1 teaspoon of flour.
In a large bowl, whisk together the flour, sugar, cornmeal, baking powder and salt until well blended.
In a medium-sized bowl, whisk together the eggs, sour cream, oil and melted butter until creamy and well combined. Add the egg mixture to flour mixture and stir just until combined. A few small lumps are okay. Gently mix one cup of blueberries into the batter.
Transfer the batter to prepared skillet. Top with the reserved 1/4 cup of blueberries.
Bake until top looks golden brown and a toothpick inserted in center comes out clean, about 35-45 minutes. Let cool in pan for 10 minutes.