Ingredients:

2 cups crimini mushrooms
2-3 sprigs fresh rosemary
1/2 teaspoon salt
1/4 teaspoon black pepper
1 tablespoon olive oil
1 tablespoon balsamic vinegar

Directions
  1. Preheat the oven to 450F.
  2. Use a moistened kitchen or paper towel to rub of any dirt from the mushroom caps. Note: Do not rinse the mushrooms! They are extremely absorbent and will soak up the water, which will dilute their flavor taste. The wet towel technique works just fine.
  3. Place the whole mushrooms, top side down, on a baking sheet.
  4. Strip leaves from rosemary stems.
  5. Drizzle mushrooms with olive oil and season with salt, pepper, and rosemary.
  6. Bake for 10 to 15 minutes, or until the mushrooms have softened and are beginning to brown.
  7. Before serving, drizzle all the mushrooms evenly with balsamic vinegar. Enjoy!

Source: Greatist