Preheat oven to 400°. Place a 12" cast iron skillet in the heated oven while making the batter.
In a large bowl, whisk together dry ingredients until mixed and create a well in the middle of the bowl.
In a small bowl, whisk together sour cream, milk, and eggs. Pour wet ingredients into the well, and with a wooden spoon, gently stir until incorporated into dry ingredients. Do not overmix. Stream in butter and stir, again, gently until evenly incorporated.
Carefully, remove skillet from the oven. Brush the canola oil onto the bottom and sides of the skillet. Pour batter into the skillet, smooth over the top with an icing spatula or a knife and bake for 20-25 minutes, or until the cornbread is golden, slightly browned along the edges and a toothpick comes out clean when inserted into the center. Serve immediately and enjoy.