First, pit or stone the fruit where necessary, and cut any larger fruit into coarse pieces.
Place the prepared fruit into a bowl to macerate in the sugar for 24 hours.
Transfer the fruit and its juices to a saucepan with a splash of water, bring to a boil, and allow to boil for 5 minutes.
Let the mixture rest for 24 hours, then repeat the previous boiling process two more times (over the next two days). Make sure never to cover the pot during or after cooking, as condensation droplets falling back into the syrup will ruin the preserve.
Once the final cooking cycle is complete, stir the mustard essence into the mixture and ladle into airtight, sterilized jars.
