Whole button mushrooms are transformed when they are cooked on high heat with just a bit of balsamic vinegar.
Pre-heat grill with a cast iron grill pan on grates.
While the grill heats, clean mushrooms under running water to remove dirt. I like the stems, but if you don't, remove them.
In a bowl, toss mushrooms in olive oil and balsamic vinegar - make sure they are evenly coated.
Add mushrooms to grill pan (be careful to avoid oil splatters). Turn as needed to get them heavily charred but not burned.
Remove from grill (I recommend using long handled tongs to keep from losing them into the grill grates) and serve as a side dish with dinner.
The prep time is deceptive - I've included the time needed to bring the grill and the pan up to roasting temperature. Actually hands on time is something under 3 minutes to wash and set the mushrooms into the marinade.