Gently heat the chicken stock in a medium pot and bring to simmer. Stir in saffron threads and take off the heat. Allow the saffron to infuse in the stock while you prepare the rice.
Place the rice in a sieve and rinse vigorously under running water to remove the starch. Set aside.
In a large pot, gently melt the butter and then add the olive oil. Pour in the rice and stir with a wooden spoon, gently coating all the grains with the butter mixture. Cook off rice on medium heat for a minute or two.
Add the saffron-infused chicken stock and stir gently. Cook over low heat until the stock has been absorbed and rice is tender for approximately 15 minutes.