Using a box grater, grate the tomato into a medium bowl, discarding the tomato skin.
Heat the oil in a medium heavy skillet over medium-high heat. Add the onions and saute until translucent, about 5 minutes. Add the garlic and cook for 1 minute. Stir in the rice and cook until slightly toasted, about 3 minutes.
Add the broth, tomato sauce and grated tomato and bring to a HYPERLINK "http://www.foodterms.com/encyclopedia/boil/index.html" boil . Add the serrano, cilantro sprig and salt, to taste. Bring to a boil, reduce the heat to medium and HYPERLINK "http://www.foodterms.com/encyclopedia/simmer/index.html" simmer until the liquid is absorbed and the rice is tender, about 15 minutes.
Turn off the heat under the skillet. Cover the rice and let stand for 8 minutes. Fluff the rice with a fork, transfer to a serving bowl and serve.
Recipe courtesy Marcela Valladolid