After about 12/16 minutes (depending on the desired consistency of the rice), turn off the heat and add the butter or mascarpone (taken directly from the refrigerator), add also the grated Parmesan and stir in quickly and vigorously to achieve the desired creaminess. At this stage it may be necessary to add a little extra stock. Taste and check the saltiness, and adjust if necessary. If no salt was added to the stock previously, some fine or flaked salt may be added at this point.