Grease an 8x8-inch baking dish with butter or cooking spray.
Soak Cornmeal
In a medium bowl, whisk together the yellow cornmeal and the boiling water. Let it stand until it cools to room temperature, about 20 minutes.
Mix Dry Ingredients
In a separate bowl, whisk together the all-purpose flour, baking powder, granulated sugar, and salt.
Mix Wet Ingredients
Once the cornmeal mixture is cool, whisk in the eggs, milk (or buttermilk), sour cream and melted butter and mix well.
Combine Wet and Dry:
Add this wet mixture to your dry ingredients and stir until just combined. Don't overmix.
Add Extra Ingredients:
Fold in the corn kernels.
If using, add the shredded cheddar cheese and diced green chiles, making sure they're evenly distributed in the batter.
Transfer to Pan:
Pour the batter into the prepared baking dish, smoothing out the top with a spatula.
Bake:
Place the baking dish in the preheated oven.
Bake for about 40 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean, top is evenly browned, and the casserole is starting to pull away from the sides of the pan.
Cool and Serve:
Let the casserole cool for a few minutes before slicing.
Video
Notes
You can use either whole milk or buttermilk for this recipe. Buttermilk will give it a tangier flavor.
Feel free to add in other vegetables or spices. Just make sure they're finely chopped so they mix well.
Serve warm, optionally garnished with a little extra sour cream or cheddar cheese.