Preheat oven to 425 degrees and place a large cast iron skillet inside while preheating. Make sure to grease the skillet with vegetable oil so that the cornbread does not stick.
In a large bowl, mix together cornmeal, flour, salt, baking powder, and baking soda. I find a simple fork does the trick.
Combine buttermilk, eggs, maple syrup, vegetable oil and melted butter. lastly add in the diced jalapenos. Combine the wet and dry ingredients and mix.
Remove the hot cast iron skillet from the oven (be very careful!). Reduce oven temperature to 350 degrees. Pour the batter into the skillet and bake in center of oven. Bake for 15 minutes.
Carefully open the oven and top the cornbread with sliced jalapenos and remaining shredded cheddar. Bake for an additional 10 minutes. Make sure the center of the cornbread is firm. While waiting mix together the reserved melted butter and remaining maple syrup for glazed topping.
Remove cornbread from the oven carefully and brush on the maple butter glaze. Allow to cool slightly and serve warm.