In a saucepan over medium-low heat melt the butter. Add the rice and sugar. Mix briefly to coat the rice with the butter and sugar. Add half the lime juice, and stir for 1 minute. Add water and salt.
Bring the rice to a boil over high heat. Reduce heat to medium-low, cover with a tight-fitting lid, and simmer until the rice is tender, 20-25 minutes.
Remove from heat and sprinkle the rice with the cilantro, the rest of the lime juice, and more salt if needed (I've never added more salt). Fluff rice with a fork. Cover and let sit for 5 minutes before serving.
Source: Muy Bueno cookbook