Preheat oven to 400°F. Place garlic on foil; drizzle with 1 tablespoon oil. Wrap garlic in foil; roast until soft, about 20 minutes. Heat remaining 3 tablespoons oil in large pot over medium-high heat. Add spinach and garlic with oil from foil packet. Saute until spinach is wilted, about 2 minutes. Season with salt and pepper. Transfer spinach to bowl and serve.