Caramelized onion portobello mushroom caps

 

5 portobello mushrooms, residual stem removed
1 large red onion, sliced thinly but long in length
1-2 T olive oil
1-2 T balsamic vinegar
1/2 T brown sugar
shredded mozzarella cheese
salt and pepper


Preheat oven to 400 degrees. Place washed and well-dried mushroom caps bottom side up on pan. Bake for 15 mins, blotting with a towel as needed. Meanwhile caramelized the onion in the oil, adding the balsamic vinegar, brown sugar, and salt and pepper to taste once softened.

Fill baked mushrooms with onions. Top with cheese and broil for 2 mins, watching very closely to prevent burning.