Place the saffron threads in a small bowl, pour over 2 tbsp (30 ml) boiling water, stir gently and leave to infuse for 10–15 minutes until the liquid turns a deep golden-orange.
Put the basmati rice in a fine sieve and rinse under cold running water until the water runs clear; drain well.
Melt the unsalted butter in a medium saucepan over a medium heat. Add the drained rice and cook, stirring constantly, for 2–3 minutes until the grains are lightly toasted and fragrant.
Pour in the stock (or water), the saffron infusion and the salt. Stir gently, then bring to the boil over a medium-high heat.
Once it comes to the boil, reduce the heat to the lowest setting, cover with a tight-fitting lid and simmer undisturbed for 15 minutes.
Remove the pan from the heat and leave, still covered, for 10 minutes to steam and absorb any remaining liquid.
Fluff the rice gently with a fork and serve straightaway.