Place the purée, juice and water in a saucepan over medium heat and bring nearly to a boil. Remove from heat.
In a bowl, whisk the yolks, sugar and cornstarch until smooth. Temper the egg mixture with the hot liquid (add just a little liquid at first to warm up the eggs without cooking them, then combine fully), return to the heat and allow to come to a boil, stirring the whole time. Once the mixture has boiled for about 20-30 seconds, remove it from the heat and add the butter. Whisk until the butter is melted and allow to cool completely. Chill and serve with fresh scones or as a pie filling.
Yield: approx. 1L of curd