Place a 9-inch or 10-inch cast iron skillet or a 9-inch round or square cake pan in a cold oven. Preheat oven to 400°F, leaving the skillet or pan in the oven while it heats. Meanwhile, whisk together the cornmeal, flour, sugar, baking powder, salt, and baking soda in a large bowl.
Add the buttermilk, melted butter, and eggs.
Stir to combine. Fold in jalapeño, cheese, and chives.
When the oven has come to temperature, pour the oil into the hot skillet or pan. Use a brush to evenly spread the oil. Pour batter into the hot, greased skillet. Bake for 20-25 minutes, or until golden brown and a toothpick comes out clean.
Notes
Buttermilk Substitute: In a pinch, you can make your own buttermilk at home to use in this recipe. To do so, pour either 1 ½ tablespoons of freshly squeezed lemon juice or 1 ½ tablespoons of white vinegar into a large measuring cup. Add enough whole milk to equal 1 ½ cups of liquid. Give it a stir, let it sit for about 5 minutes, and then use it in the recipe as directed.