Step 1 Rinse the rice several times until the water runs clear. In a large saucepan, combine the water and hazelnut milk with the salt, cinnamon stick and zest, and bring to a simmer over high heat.
Step 2 Place the rice in a separate heavy saucepan. Stir in 2 cups of the simmering nut milk and bring to a simmer over medium-high heat. Cook, stirring occasionally, until the rice has absorbed almost all the liquid.
Step 3Continue cooking the rice as you would a risotto, adding the nut milk, a ladleful at a time, as the rice begins to swell and absorb the liquid. When the rice is almost tender, stir in the brown sugar and vanilla extract. Continue cooking, stirring frequently to make sure the rice does not stick to the bottom of the pan and burn, 25 to 30 minutes total. The finished rice will be thick and creamy.
Step 4Move the rice to a medium bowl and cover with plastic wrap pressed flat against the surface (this will prevent a skin from forming). Refrigerate until chilled, and serve garnished with shaved dark chocolate.