4 large Portobello mushroom caps
2 large cloves garlic, cut into slivers
1 ounce Romano, Parmigiano-Reggiano, or other firm cheese, cut into slivers
1 sprig fresh rosemary, leaves stripped off the stem
½ cup balsamic vinegar
½ tsp course salt
½ tsp black pepper
1 cup extra- virgin olive oil
With a moist paper towel, wipe the caps clean. Insert garlic slivers, rosemary and cheese slivers in some of the gills.
In separate bowl combine vinegar, salt, pepper. Whisk in olive oil. Pour marinade over mushrooms, spooning marinade into mushroom gills. Let marinate in refrigerator, covered, for as little as 30 minutes or as long as 3 hours.
Preheat grill to high. Remove mushrooms and arrange gill side down. Grill for 3 minutes, then invert the portobellos and spoon on some of the reserved marinade. Continue grilling until caps are browned and very tender, 4 to 6 minutes.