Marinade (enough for 6 large portabella caps):
1 cup balsamic vinegar (you may also substitute part white wine or other good-tasting vinegar)
2 tablespoons olive oil
1 teaspoon dried basil
1/4 teaspoon kosher salt
1/4 teaspoon white pepper
2 garlic cloves, minced
For each sandwich:
toasted hamburger bun or roll
cheese (Swiss is a good choice)
Marinade the mushroom caps for at least one hour. Grill (or pan-fry) for 5 minutes or until tender. Build your sandwiches like a burger and enjoy!
Notes: I highly recommend grilling the mushrooms if you are able, it adds a nice flavor. One thing to keep in mind is that the mushrooms are rather like sponges: as soon as you squeeze them (say, to bite into the sandwich), a lot of the juices squeeze out and into the bottom bun. So, if you don't like soggy buns, you might try broiling the cheese onto the bottom bun, or putting the lettuce on the bottom to protect that bun. At any rate, it's a juicy sandwich, so keep those napkins handy!