Preheat oven to 400°F.
Rinse, remove stems, and halve chiles. Scrape out seeds with the tip of a knife. Dice chiles.
In a medium bowl, beat egg slightly with a fork.
Add buttermilk, yogurt, and chiles to the egg. Mix until smooth.
In a large bowl, mix flour, cornmeal, sugar, baking powder, and salt.
Add wet mixture to dry ingredients. Blend with a rubber spatula or mixing spoon until just moist. Small lumps are OK. Do not overmix or cornbread will be too dense.
Coat the baking dish with non-stick spray. Pour in batter.
Bake on middle rack of oven until edges are lightly browned and a toothpick inserted in the middle comes out clean. This will be about 25–30 minutes. Remove from oven. Let cool in pan for 10 minutes before serving.