Set up grill for indirect cooking and preheat to 325-400ºF (temperature depends on other foods being grilled)
Place a 10 inch cast iron skillet on 'cool' side (not over coals) of grill and allow skillet to heat with cooker lid closed until very hot
While skillet is heating - Place the cornmeal, flour, sugar, baking powder, and salt in a large bowl and mix to combine
Melt butter in a small bowl in the microwave
In a small bowl, beat together the milk and egg until well combined
Add the milk/egg mixture to the cornmeal mixture and stir with a fork until combined
Slowly add the melted butter to the batter stirring until just combined
Add 1 Tbs of butter to the hot skillet and 'swirl' until the bottom and 1 inch up the sides are coated
Pour the batter into the hot skillet (batter should sizzle) - Spread batter to even out the batter if necessary
Allow cornbread to cook with the cooker covered for 20-40 minutes or until a toothpick inserted into the center comes out clean (cooking time varies on cooker temperature)
Remove from cooker and allow to rest for 10 minutes before cutting
NOTE: You can prepare cornbread completely in the oven - Preheat oven to 400ºF with skillet inside and follow directions otherwise as written - Cooking time will be approximately 20-25 minutes