Heat the butter in a heavy saucepan over medium heat. Add the onion; sauté, stirring, until the onion begins to wilt, about 3 minutes. Add the rice; stir to coat. Cook, stirring, until the grains of rice are starting to turn translucent, about 2 or 3 minutes.
Add the broth all at once, along with a pinch of salt. Raise the heat, cover the pan, and bring the bro