Preheat your gas grill to 350°F. If you’re using a charcoal grill, light your fire 20-30minutes in advance.
Melt your butter in your cast iron skillet over medium heat on your side burner, or straight on your grill top. Carefully keep an eye on it and stir constantly. About 30 seconds after melting, you’ll see it start to foam and bubble. Keep stirring.
Keep stirring until you get an even brown color, then pour it out of the pan and into a large bowl.
In the large bowl, toss your brussel sprouts and hazelnuts with the browned butter, salt, and pepper.
Add the brussel sprouts mixture back into your cast iron pan, face down in a single layer.
Place on your grill and roast for 10 minutes. Check about half-way through and give your pan a shake to ensure the brussels aren’t sticking. You’ll know they’re done when the brussel sprouts are tender but not mushy.
Remove from the grill and sprinkle the finely grated lemon zest and parmesan.
Serve and enjoy.
Swap out the hazelnuts for a different type of nut, such as sliced almonds.
Make your side dish into a main by adding bacon or chorizo.
Amp up the flavor by swapping the paremesan for crumble feta.