Preheat your smoker to 275-300°F.
Add the butter, balsamic vinegar, salt, and pepper to the cast iron skillet. Place it on the smoker to let the butter melt, and the pan preheat for up to 30 minutes.
Wash and dry the Brussels sprouts. Remove any shriveled leaves. Trim the stalk of the individual sprout down. Cut each sprout in half lengthwise.
Remove the balsamic and butter mixture from the smoker, stir, and sprinkle 1 cup of Parmesan evenly over the top.
Place the sprouts, cut side down onto the balsamic and butter mixture, pressing down slightly.
Return the skillet to the smoker and cook for 30-60 minutes.
Once you have a nice brown crust form on the bottom of the sprouts, and are able to to pierce them easily with a fork, they are done. Remove from the smoker and rest for 5 minutes.
Transfer to a serving bowl, sprinkle with the remaining ½ cup Parmesan, and drizzle with balsamic glaze if using. Serve warm.