Prepare the ingredients: wipe the mushrooms clean with a damp paper towel and slice them in half. Chop the onions and garlic.
Heat 1 tablespoon olive oil in a large heavy skillet over medium to high heat. Once the oil is hot, add the onions and garlic. Cook for a few minutes until they begin to turn soft.
Add the remaining oil to the skillet and once it's hot, add the mushroom pieces. Be sure to leave enough room between each piece. Let them cook for a few minutes undisturbed and then give them a stir.
Stir in the balsamic vinegar and cook for about 2 minutes longer over medium to low heat until the mushrooms begin to absorb the vinegar.
Season to taste with sea salt and black pepper and garnish with fresh herbs.
Notes
Store leftover mushrooms in the refrigerator for up to 4 days.See the article above for recipe tips, serving suggestions and more!