Start by cleaning the baby bella mushrooms. Gently wipe them with a damp cloth and slice into halves or quarters.
In a large skillet, heat the butter and olive oil over medium heat until melted and bubbly.
Add the minced onion to the skillet and sauté for about 3-4 minutes until translucent. Then add the minced garlic and sauté for another minute.
Add the sliced mushrooms to the skillet, stir to coat, and cook for about 5-7 minutes until tender and browned.
Pour in the balsamic vinegar and soy sauce, stir, and sprinkle in the brown sugar, parsley, and rosemary. Let simmer for 3-5 minutes.
Taste and adjust seasoning if necessary, then remove from heat and serve warm.
