I named this cocktail after the Princes – as in the food writer Rose and her husband Dominic who brought me some fruit. This infusion lasts well and can be used for all sorts of drinks. I've used the poaching liquor from the cooked quinces in the recipes above as the sweetener here.
500g quinces, coarsely grated
Mix the quince, gin and sugar together; store in an airtight container for 3-4 weeks.
Strain through a fine sieve and store in airtight bottles until required.
To make the cocktail for two, use 150ml of the quince gin mixed with 150ml quince cooking liquor, the juice of 1 lemon and an egg white.
Shake this in a cocktail shaker with ice; pour into suitable serving glasses.