Combine saffron threads and hot water in a small bowl, stir gently, and let bloom for 10–15 minutes until the liquid turns a golden-orange hue.
Place the basmati rice in a fine-mesh sieve and rinse under cold running water until the water runs clear; drain well.
Melt unsalted butter in a medium saucepan over medium heat. Add the rinsed rice and sauté, stirring constantly, for 2–3 minutes until the grains are lightly toasted and fragrant.
Pour in the broth (or water), the bloomed saffron mixture, and salt. Stir gently to combine and bring to a rolling boil over medium-high heat.
Immediately reduce heat to the lowest setting and cover the saucepan tightly with a lid. Simmer undisturbed for 15 minutes.
Remove the saucepan from heat and keep the lid on. Let the rice rest, still covered, for 10 minutes to steam and finish absorbing moisture.
Remove the lid, fluff the rice gently with a fork, and serve immediately.