Position rack in center of oven and preheat the oven to 350°F.
In a medium saucepan, melt the butter over medium heat. Add the onion and cook, stirring, until soft, about 3 to 4 minutes.
Add the rice and cook, stirring, until opaque (cloudy), and nutty in aroma, about 2 minutes.
Add the water, chicken broth, and salt and bring to a boil.
Cover the pan with a tight-fitting lid. Using oven mitts or pot holders, transfer to the oven, and bake until the rice is tender and the liquid is absorbed, about 25 to 30 minutes.
Using oven mitts or pot holders, remove the pan from the oven and let sit, undisturbed, for 5 to 10 minutes.
Fluff the rice with a fork and stir in the scallions, if desired. Serve hot.
YIELD: 4 1/2 cups, serving 6