Soak the sheets of gelatine in cold water for 10 minutes. In a heavy-bottomed saucepan, use a whisk to mix the egg yolks with the sugar and Vin Santo; cook over a low heat, whisking until the zabaglione becomes light and frothy. Remove from the heat, add the well-squeezed gelatine and stir until it dissolves. Leave the zabaglione to cool, stirring occasionally. In a bowl, whip the cream with an electric hand mixer (both cream and whisks should be nice and cold) and, a little at a time, fold it into the cold zabaglione delicately so the mixture remains as light as possible. Crumble the Brutti ma Buoni biscuits and incorporate ¾ into the zabaglione. Wash and dry the nectarines, remove their stones and cut them into small pieces (set a spoonful aside to use as a garnish at the end). Divide the pieces of nectarine between 4 glasses, cover with the zabaglione mousse and put them in the fridge for a couple of hours. Before serving, garnish with the remaining crumbled Brutti ma Buoni and the pieces of nectarine you set aside.