Heat the butter and oil in a deep saucepan until they start to foam. Add the rice and stir until all the grains are coated. Pour in the boiling water and stir. Add the salt and the saffron. Bring the water back to the boil. Add the raisins.
Reduce the heat to a very gentle simmer and cover the pan with a tight fitting lid. Cook until all the water has been absorbed (about 20 minutes). Turn off the heat and leave the rice to stand for 5 minutes before serving.