Tip all the fruit into a bowl, then sprinkle over the icing sugar, lemon juice and elderflower cordial. Stir and leave to macerate for 1 hr.
Whisk the double cream and vanilla extract, if using, to soft peaks using an electric whisk, then fold through the Greek yogurt and lemon zest. Gently fold three-quarters of the summer fruits through the cream mixture. Divide most of the remaining fruit between four dessert glasses, then spoon over the cream mixture and top with the rest of the fruit before serving. Will keep chilled overnight.
