Heat the butter and oil together in a large saute pan over medium heat. Add the onion and saute until soft. Do not brown, they should be translucent. Add the rice and saute for a further 3 to 5 minutes making sure the rice is well coated, Using a ladle, add about 1/2 cup of stock to the rice and stir over a medium heat until the rice is almost dry and all the stock has been incorporated. Repeat this process until the rice is cooked but still has a slight bite. The rice should be creamy and moist, not runny, and the cooking time should be around 30 minutes.
Just before serving, fold in the crabmeat, chopped chives, and Parmesan. Drizzle sparingly with white truffle oil.