First, remove the stem and any woody or hard bits from the bottom of the mushrooms.
Then gently wash them under running water, removing any dirt or soil. Pat dry.
Place the cleaned mushrooms in a shallow dish.
In a small measuring cup, combine the balsamic vinegar, soy sauce, chopped rosemary and thyme.
Pour this mixture over the mushrooms and allow to soak for 5-6 minutes on each side.
In a large enough sauce pan or skillet to fit the mushrooms, melt the butter over medium heat.
Cook the mushrooms for 3-4 minutes on each side. Drizzle the remaining sauce from the pan over the mushrooms during the last couple minutes of cooking.
Notes
If you'd like to make this recipe vegan/dairy-free, swap the butter for a cooking oil instead.