1 1/2 pounds fava beans (or 3/4 cup frozen beans)
2 tablespoons sherry or red wine vinegar
2 tablespoons extra-virgin olive oil
1 medium garlic clove, finely minced (about 1 teaspoon)
2 sprigs fresh rosemary
1/2 teaspoon salt
1/4 teaspoon freshly ground black pepper
Bring a pot of salted water to a boil. While the water heats, remove the fava beans from their long pods. Once the water boils, add the fava beans and cook until bright green and just tender, about 3 minutes. Drain and immediately rinse under cold water. Pop the bright green fava beans out of their casings and set aside.
In a pint jar, combine vinegar, olive oil, garlic, rosemary sprigs, salt, and pepper. Place a lid on the jar and shake to combine the vinaigrette. Pour prepared fava beans into the jar of vinaigrette. Replace lid and shake to coat the fava beans. Let stand at least 15 minutes before serving.