Serve with our Poached Dried Apricots and Currants.
Rub together sugar, zest, and vanilla seeds in a medium heatproof bowl using your fingers. Add yolks. Whisk until pale and creamy. Whisk in Vin Santo and salt. Set bowl over a pan of simmering water, and whisk until mixture thickens and doubles in volume, about 10 minutes. Serve warm.