Step 1Cut the fruit in half vertically and discard the pits. Cut them into slices about three-eighths of an inch thick. In a small bowl, toss the slices with two tablespoons of sugar (or to taste) and a squeeze of fresh lemon juice. Set aside to macerate while you prepare the risotto.
Step 2In a small saucepan, heat the water and milk together until hot but not boiling. Add the remaining sugar and the salt. Set the hot milk aside. In a heavy, 2-quart saucepan, melt half the butter. Add the rice and sauté until the grains are opaque and make a clicking sound against the side of the saucepan, less than 1 minute. Add the wine and cook over low heat, stirring until the rice absorbs it.
Step 3Add the hot liquid 1 large ladleful at a time to the rice over low heat. Wait until all the liquid is absorbed before adding the next ladleful of liquid. Stir frequently, if not constantly, using a silicone spatula or angled wooden spatula to sweep the bottom of the pan to prevent the rice from sticking. When all the liquid is absorbed the rice should be tender with no chalky sensation (if the rice isn’t quite done, add additional hot milk as needed to finish the rice). Remove from the heat and beat in the remaining butter. Adjust sugar and salt as needed. Add the vanilla if you like.
Step 4Spoon the fruit into individual serving bowls. Break the chocolate bar into irregular pieces and insert them into the rice so they stick up. Spoon the nectarines over the rice along with their juices. Finish with a scattering of amaretti crumbs.