Preparation
Preheat oven to 400 degrees
1. Place balsamic vinegar in small pot and place on stove. Cook over low heat. The goal is to allow vinegar to cook until reduced to 1 cup, so note how far up the vinegar fills pot. This should take about 15 minutes.
2. While vinegar is reducing, place portobello caps, gill side up, in small baking dish.
3. In small bowl, mix gorgonzola, Parmesan, bread crumbs, parsley and egg until well-combined.
4. Spoon gorgonzola mixture into mushrooms. Cover and bake in preheated oven 20 minutes or until mixture is bubbly.
5. When vinegar is reduced, remove from stove and stir in rosemary.
Presentation: To serve, place stuffed mushrooms on a serving plate and spoon vinegar reduction over mushrooms. Serve hot.