Place the saffron threads in hot water in a small bowl and allow the saffron to steep until golden in color, 10-15 minutes.

Meanwhile, rinse the rice with cold water until the water runs clear. Drain well and set aside.

In a medium pot, melt the butter on medium-high heat. Add the onions and cook until softened, about 5 minutes. Transfer the rinsed rice and the steeped saffron with the hot water over the cooked onions. Season with salt and pepper, and stir to combine until the rice mixture looks yellow.

Add the water and bring the mixture to a boil. Reduce the heat to low, cover with a tight-fitting lid and cook for 15 minutes.

When the time is up, remove from the heat and allow the rice to steam for 10 minutes. Then uncover and fluff with a fork.

Serve warm with fresh parsley, if desired.