Caramelising onions brings out their natural sweetness, while the balsamic vinegar adds a tart, sweet note. Together they create perfect harmony, a sweet and slightly sour ice cream that I regularly prepare at home for dinner parties. It certainly makes a good conversation piece!
Put the onions in a pan of boiling water, simmer for 5 minutes, then drain. Repeat, then dry well on a kitchen towel. Melt the butter and
Whisk the egg yolks, whole egg and the remaining sugar together until the mixture whitens. Put the milk, cream and onions in a clean pan and bring to the boil, then pour on to the egg mixture a little at a time, stirring. Return to a clean pan and cook over a gentle heat, stirring all the time with a wooden spoon, until the mixture is thick enough to coat the back of the spoon. Be careful not to let it boil.
Strain the mixture into a clean bowl and stir in the balsamic vinegar. Cool the ice cream quickly by standing the bowl in a larger bowl of iced water and stirring until cold. Churn in an ice-cream maker until the mixture resembles semi-whipped cream, then freeze until firm. If you don’t have an ice-cream maker, pour the mixture into a bowl and place in the freezer. After 30 minutes, when the mixture is beginning to set, remove from the freezer and beat well with an electric beater or hand blender to disperse any ice crystals, then return it to the freezer. Repeat this 2 or 3 times, then leave until the ice cream is set firm.