Place spinach in a small metal colander. Fill a slightly larger pot with one to two inches of salted water. Place the colander inside the pot and cover. Bring the water to a boil over high heat, and steam spinach until tender, about four to five minutes. Remove spinach from pot.
Place raisins in a bowl of lukewarm water, enough to cover, and let sit for 30 minutes. Drain and rinse raisins.
In medium pan over medium-high heat, warm garlic and olive oil. Add spinach and sauté for about two minutes. Add raisins, salt, and pepper. Immediately stir in pecorino. Serve warm.
