Preheat your oven to 400 degrees.
Coat a nonstick skillet with cooking spray and heat over4 med-high heat. Saute onions, corn, and jalapenos until corn is slightly charred. Approximately 5 minutes.Set aside and cool to room temperature.
Sift flour, sugar, baking powder, baking soda and salt into a medium bowl, add in cornmeal and whisk to blend.
In a small bowl, whisk buttermilk, egg, and oil.Add the wet ingredients to the dry ingredients and stir with a wooden spoon. Fold in the corn mixture.
Coat a 10 inch cast iron skillet with cooking spray and pour in the mixture. Level and smooth the top with a spatula.
Bake for 15 minutes, until the top is lightly golden and the center is just firm to the touch.
Transfer the pan to a wire oven rack to cool for a few minutes before cutting the corn bread into wedges.