1. Place a 12-inch cast iron skillet on the center rack of the oven and preheat to 375 degrees F.
2. Combine milk and lemon juice and let sit for 5 minutes.
3. In a large bowl, whisk together cornmeal, salt, baking powder, and baking soda.
4. Whisk eggs into soured milk. Drizzle in oil and all but 1 tablespoon of the melted butter.
5. Whisk wet ingredients into dry ingredients until well mixed but slightly lumpy.
6. Pour remaining butter into hot skillet and swirl to coat bottom and sides. Pour batter into prepared skillet. Bake until cornbread is lightly browned on top and a toothpick inserted into the middle comes out clean (about 45 minutes).