In a colander under cold-running water, rinse the rice and transfer to a medium heavy saucepan with a tight-fitting lid. Pour in 2-1/2 cups cold water and bring to a boil over high heat. Reduce the heat to medium low, cover, and cook for 20 minutes. Remove the lid, fluff the rice with a fork, and add the butter, 1 teaspoon salt, and the saffron. Cover and let sit for 5 minutes. Season with more salt (if needed) and freshly ground black pepper before serving.