Place blueberries, sugar, lime juice and zest into a preserving pan (or one of equivalent size).

Over a gentle heat, dissolve the sugar, stirring regularly (do not simmer).

One the sugar has dissolved crush about half of the blueberries with a potato masher leaving the other half whole.

Then turn up the heat to bring the pan to a rolling boil and set a timer for 8 minutes (stir continuously with a wooden spoon to stop the jam catching on the bottom of the pan).

Test for set by removing jam from the heat and putting a teaspoon full of jam on a chilled saucer.

Place saucer in fridge for about 30 seconds, then push your finger through the jam which should form a soft gel like crinkle (it’s better to under cook than over cook).

If the jam hasn’t reached setting point yet, cook for another minute and repeat test until ready.

Pot up into hot sterilised jars and screw on lids immediately. (I find a small fruit ladle and jam funnel useful for this.)

Allow jam to cool before using and keep in a cool dark place.

Once opened jam should be kept in the fridge and used within about 3 months. Unopened jam is best eaten in the first year but will last years.