Put all the ingredients in a large pan and bring to a simmer. Cook, uncovered, for about 1 hour, stirring occasionally. To test if the pickle is ready, drag a wooden spoon across the surface – if a channel remains for a few seconds, without being filled with excess vinegar, it’s ready.
Leave the pickle to cool down a little, then spoon into sterilised jars. Seal and leave to cool completely. Label and store in a cool, dark place for at least 3-4 weeks to mature before giving away or eating. Once opened, the pickle will keep in the fridge for up to 6 weeks.
Cook’s tip: to sterilise jars, wash the glass and lids in warm soapy water, then rinse well with warm water. Dry thoroughly with a clean tea towel, then place upside down on a baking tray and put in an oven preheated to 180°C, fan 160°C, gas 4 for at least 5 minutes. Carefully fill with the pickle while the jars are still hot.