Preheat your oven to 400 degrees F. Set your 10-inch cast iron on the stove.
In a large bowl, whisk together the flour, cornmeal, brown sugar, baking powder, baking soda and salt. Add the shredded cheddar and diced jalapeños and toss the dry ingredients together.
Place the skillet over medium-high heat and add the butter. When melted, swirl it around so that it coats the entire bottom of the pan, as well as the sides. Turn the heat off.
In a medium bowl or a large measuring cup, measure out the buttermilk, whisk in the eggs, and neutral oil. Lastly, pour in the melted butter (some butter remaining in the pan is great! don’t scrape it clean with a spatula). Whisk until combined. Pour the wet ingredients into the dry and mix no flecks of flour remain, being sure not to overmix the cornbread. Pour the batter into the buttered cast iron skillet and immediately transfer to the oven to bake until golden brown on top and until a skewer inserted into the center comes out clean, about 25 to 30 minutes
To Make the Scallion Butter:
In a small skillet set over medium heat. Add the scallions and cook until bright green and softened, about 1 minute. Add a pinch of salt and mix.
In a small bowl, add the softened butter and scallions. Mix together until combined. Add to a small bowl and sprinkle the top with flaky sea salt.
Serve with warm cornbread.
Notes
Other Cheese Options: You could use other types of cheeses like smoked gouda, fontina, smoked cheddar or swiss. Equipment: 10 1/4-inch Le Creuset Cast Iron Skillet | Silicon Spatula | Stainless Steel Bowls | Chef's Knife | To Freeze Cornbread: You can make ahead and freeze cornbread. Allow to come to room temperature and then wrap tightly with plastic wrap. Transfer to the freezer and keep up to 1 month. Thaw in the fridge overnight and then warm up in a 200 degree oven.