Mix dry muffin mixture, egg, and milk together - stirring just until moist. Let sit for 5 minutes.
Place batter into a ziptop plastic bag and keep refrigerated until ready to cook.
Making Your Pie Iron Cornbread
Prepare your cooking area by lighting charcoal briquettes.
Warm up pie irons by placing on top of briquettes.
Once pie irons are warm and briquettes are white hot, butter insides of pie irons and squeeze one quarter of mixture into each pie iron. Optional - add any extras on top of the batter at this point.
Close pie irons, clamp shut, and place in fire for 4 minutes. Flip to other side and cook for 4 more minutes. Check for doneness (cornbread will be golden brown) and if necessary cook 1-2 minutes more.