Preheat the oven to 400 degrees F

Heat a 12-inch cast-iron skillet on the stovetop over medium heat. Add 1/4 cup butter and allow to melt.

Reserve the melted butter for later use, carefully wipe out the pan, and place in the oven to heat.

In a bowl, combine the milk, buttermilk, egg and melted butter. Add wet ingredients to cornbread mix. 

Add combine the cornmeal and mix until lumps have dissolved.

Fold in the cheese, corn and poblanos.

Carefully remove the skillet from the oven and add the remaining 2 tablespoons butter until it sizzles. 

Coat the pan with the butter and quickly pour the cornbread batter into the skillet. 

Place the skillet in the oven and bake until golden brown, about 20 - 25 minutes.

Remove from the oven and let cool slightly before slicing. Serve warm.