1. Bring the broth to a very slow, steady simmer on a burner near where you'll be cooking the risotto.

2. Put 1 tablespoon of butter, the vegetable oil, and the chopped onion in a broad, sturdy pot, and turn on the heat to medium high. Cook and stir the onion until it becomes translucent, then add the rice. Stir quickly and thoroughly until the grains are coated well.

3. Add ½ cup of simmering broth and cook the rice, stirring constantly with a long wooden spoon, wiping the sides and bottom of the pot clean as you stir, until all the liquid is gone. You must never stop stirring and you must be sure to wipe the bottom of the pot completely clean frequently, or the rice will stick to it.

4. When there is no more liquid in the pot, add another ½ cup, continuing always to stir in the manner described above. Maintain heat at a lively pace.

5. Begin to taste the rice after 20 minutes of cooking. It is done when it is tender, but firm to the bite. As it approaches that stage, gradually reduce the amount of liquid you add, so that when it is fully cooked, it is slightly moist, but not runny.

6. When the rice is about 1 or 2 minutes away from being fully cooked, add all the grated Parmesan and the remaining butter. Stir constantly to melt the cheese and wrap it around the grains. Off heat, taste and correct for salt, stirring after adding salt.

7. Transfer to a platter and serve promptly. Shave the optional white truffle over it, using either a truffle slicer or a swiveling-blade vegetable peeler. Some prefer to shave the truffle over each individual portion.