Start your grill, prepare it for indirect heat. We want it running at 200° C / 400° F.
Melt the butter slowly in a pan. Pour it into a bowl, together with everything but the dry ingredients. Whisk together until blended.
Mix the dry ingredients (corn flour, wheat flour, sugar, salt, backing powder) in another bowl and stir well.
Now mix it all together in one bowl. Whisk until homogenous.
Pour the batter into the cast iron skillet (10" / 25 cm), and smooth out the surface if necessary.
Place the skillet on the indirect side and close the lid. Let it bake for 20-30 minutes. Check to see if it is done with a wooden toothpick. Stick it vertically into the bread and pull back out. When there's no bread/dough residue sticking to the toothpick, the bread is done.
Bring it in and let it cool off for 10 minutes before serving.