Cut a thick slice off either side of each mango to reveal the large, flattish stone. Trim the flesh from around the stone, then cut away the peel, dice the flesh and add to a preserving pan. Cut criss-cross lines over the remaining mango slices, then press the skin side so that the squares of mango stand proud of the skin, like a hedgehog. Slide a knife under the cubes of mango to release, and add to the pan with the lime juice and measurement water.
Cook, uncovered, over a low heat for 8–10 minutes, stirring from time to time, until the mango is soft.
Add the lime rind and sugar and heat gently, stirring from time to time, until the sugar has completely dissolved. Bring to the boil, then boil rapidly until setting point is reached (10–20 minutes).
Turn off the heat, scoop the passion fruit seeds from the fruit with a teaspoon and stir into the jam. Allow to cool for 5–10 minutes so that the seeds will not rise in the jam, then spoon into warm, dry jars, filling to the very top. Cover with screw-top lids, or with waxed discs and cellophane tops secured with elastic bands. Label and leave to cool.