Preheat the oven to 375ºF (190ºC). Grease a 10-inch cast iron skillet with bacon fat, Crisco, or vegetable oil.
In a small mixing bowl, whisk together the flour (1 3/4 cups), cornmeal (1 1/4 cups), baking powder (1 1/2 teaspoons), baking soda (1 teaspoon), and salt (3/4 teaspoon).
In a medium mixing bowl, whisk together the sour cream (1 cup), sugar (2/3 cup), milk (1/2 cup), butter (8 tablespoons), and eggs (2) until well combined. Add the dry ingredients to the wet ingredients and mix until almost combined. Add 1 1/4 cup blueberries and gently fold in. Do not overmix.
Evenly spread the batter into the skillet and dot the top with the leftover blueberries.
Bake for about 28-32 minutes until the top is golden brown and a toothpick comes out with a few moist crumbs.
Let cool in the pan on a wire cooling rack for 15 minutes before serving.
Notes
If you use unsalted butter, add 1/4 teaspoon salt to the cornbread.
If you use frozen blueberries instead of fresh, put them in while frozen. Do not thaw. Reduce the milk by 2 tablespoons, as the frozen blueberries will release more moisture while being baked than fresh.