Preheat oven to 400°F. Place a 10-inch cast iron skillet in the oven while preheating.
Combine all the dry ingredients together in a mixing bowl. In a separate bowl, whisk the egg with the cooled butter, sour cream, and milk. Pour the wet ingredients over the dry and stir until almost combined. Add the cheddar and pimientos, stirring until just incorporated. Do not overmix.
Remove the skillet from the oven and lightly coat the bottom and sides with oil or
cooking spray. Pour batter into pan and spread evenly. Bake for 20-25 minutes or
until tester inserted into the center comes out clean. Cut into wedges and serve warm.