Preheat oven to 400 degrees. Heat a 10.25-inch cast iron skillet over medium heat. Add butter and melt. Pour butter into a medium bowl and set aside. Swirl the butte that remains in the skillet around the bottom and sides of the skillet. Set aside.
Slice one jalapeno into thin rings. Finely mince the second jalapeno.
In a large mixing bowl, add cornbread mix, minced jalapeno and 1 1/2 cups shredded cheese. Stir.
In the bowl with butter, add milk, eggs and sour cream. Whisk well then pour into the dry mixture. Mix until it just comes together. Pour the batter into the cast iron skillet.
Top the cornbread batter with the remaining 1/2 cup shredded cheddar and jalapeno slices.
Bake for 28 to 30 minutes, until a toothpick comes out dry.