Heat a large non-stick pan with 1 tbsp of olive oil and 3 tbsps of butter over medium heat.
Place the mushrooms in the pan, stem side down and cook 12-15 minutes, until mushrooms have softened and release their juices.
Flip the mushrooms and add the onion, garlic, and 2 tbsps butter. Cook 8-10 minutes, stirring occasionally, until onions start to brown. Add the wine, balsamic vinegar, and half the herbs. Season with salt and pepper, reduce the heat to medium-low, and simmer for 10-15 minutes.
Garnish the mushrooms with the remaining herbs and serve.