If you don’t have a jam thermometer, put a couple of saucers in the freezer to chill. Put all the ingredients in a large saucepan or jam pan, and cook over a medium heat until the courgettes have released their liquid and the sugar has dissolved, about 10 mins. Cook for another 10 mins, stirring often until the liquid has reduced slightly, then cook for 10-15 mins more until the mixture reaches 105C on a jam thermometer. Or, spoon a little of the jam onto one of the cold saucers. After a couple of minutes, gently push your finger through the jam – if the surface wrinkles, it’s ready. If not, return to the boil for 2 mins, then re-test using the second saucer.

Remove from the heat, skim off any froth, then leave to cool for 10 mins. Spoon into sterilised jars (see our guide). Will keep chilled for up to three months. Serve on toast as you would a marmalade.