Preheat grill to medium-high heat. Do not follow package ingredients or instructions. Instead, mix brownie mix package with 1/3 cup (75 mL) water, egg and oil until just combine. Fold in chocolate chips. Spread batter evenly in greased 9 in. (23 cm) cast-iron skillet.
Turn off one burner of grill; keeping other burner(s) on medium-high. Place skillet over the turned-off burner. Close lid; cook 15 to 20 min., until slightly crisp around edges and just set in the centre.
Spoon into bowls and top with ice cream, if desired.
Alternatively, bake brownies in the cast-iron skillet in 180 C (350 F) oven 25 to 30 min., until just set in the centre.