Place mushrooms, stem side up in shallow baking dish, cover and refrigerate 4 hrs. to 2 days.  30 min before cooking, remove mushrooms from refrigerator. Preheat oven to 450: bake 12-15 min.
Serve on rolls with pesto or mayo and roasted red peppers and mozzarella under broiler for a minute.

1/2 cup balsamic vinegar
1/2 cup doy
1/2 cup olive oil
1 tspl minced garlic
2 T. fresh rosemary or 2 tsp. dried
1 tsp. pepper
1/2 cup water