Risotto with truffle
Melt the butter in a wide, high-sided pan over a very low heat. Peel the onion and chop it finely. If your onion is larger than a golf ball, you will only need half of it.
Add the onion to the pan and cook to soften it in the butter, stirring from time to time, so that it does not colour but instead becomes translucent and silky.
Stir in the rice, folding the grains over briefly in the butter with a wooden spoon.
Pour in the wine or vermouth and let it bubble down until the liquid has pretty much disappeared.
Add a large ladleful of hot stock, turn the heat up a bit, then cook until the liquid has almost disappeared. Continue adding the stock as it boils down to almost nothing. Stir the rice often.
Season, to taste, with salt and freshly ground black pepper and add the lemon zest and juice. Continue cooking until the rice is creamy but has a little bite left in it.
Add parmesan, to taste, and stir well.
To serve, spoon the risotto into a serving dish and shave the truffle over the top. Serve immediately.