This sandwich has it all: tart balsamic vinegar that caramelizes the mushrooms and onions, oozing brie cheese and crusty, crunchy bread. This unique twist on a classic sandwich is perfect for grilled cheese lovers of all ages. Recipe courtesy of Bits and Bites Sandwich Bar, Brie Cheese Recipes, Balsamic Mushrooms, Mushroom And Onions, Buffet, Baked Brie, Brunch Recipes, Burger Recipes, Caramelized Onions