Move the oven rack to the middle position. Preheat the oven to 400°F. Spray an 8-inch square pan with nonstick cooking spray and set it aside.
Mix Dry Ingredients:
Whisk the 1 cup flour, 1 cup yellow cornmeal, ¼ cup sugar, 2 teaspoons baking powder, ½ teaspoon baking soda, and 1 teaspoon salt together in a large bowl.
Mix Wet Ingredients:
Whisk the 1 large beaten egg, ⅓ cup milk, 6 tablespoons melted butter, and 1 cup sour cream together in a large liquid measuring cup until combined.
Combine:
Pour the wet ingredients into the dry ingredients. Stir until just combined, leaving no flour streaks. Do not overmix the batter.
Add Mix-ins:
Fold in the 4 ounces of diced green chiles and 1 cup of grated sharp cheddar cheese.
Transfer:
Pour the batter into the prepared pan. Smooth it into an even layer. Dot the top of the batter with the 8 small pieces of cold butter.
Bake:
Bake for 25 to 30 minutes. The top should be golden brown, and a toothpick inserted into the center should come out clean. Move the cornbread to a wire rack.
Cool:
Let it cool for at least 20 minutes before slicing and serving.
Notes
Storage and Make Ahead
Room-temperature storage: Store leftover cornbread in an airtight container for up to 2 days.Refrigerator storage: Refrigerate the cornbread for up to four days.Freezing: Wrap each piece in plastic wrap, then place it in a freezer bag. Freeze for up to two months.Thawing: Thaw overnight in the refrigerator or at room temperature for about one hour.Reheating: Warm slices in the microwave for about 20 seconds, or reheat in a 300°F oven until heated through.Make-ahead option: The batter can be prepared a few hours in advance and refrigerated before baking.