Reducing a Fruit Paste to a Spreadable Concentrate

A fruit filling needs to be cooked down until it is thick and spreadable, not loose. Simmer the fruit with a little liquid, sugar, and citrus, stirring, until the fruit is very soft and most of the liquid has evaporated, then blitz to a smooth paste. Reducing it concentrates the flavour and keeps the filling from leaking or making the surrounding dough soggy. Citrus zest and juice lift and sharpen an otherwise flat, jammy paste. Cool it completely before spreading — a warm paste will melt the dough.