lemon verbena or lemon balm sprig, to serve (optional)
First, sterilise a large jar or bottle. Wash in hot, soapy water, then place on a baking tray and put in a low oven for 10 mins or until completely dry. Put the blackcurrants in the warm sterilised jar and set aside. Make an infusion with 500ml boiling water and the lemon verbena, then stir through the sugar. Pour over the blackcurrants, stir and leave to cool. Cover with a lid, then put in the fridge. Every day for about 5 days, gently shake the jar.
By this time, the fruit should have macerated in the sugary tea. Tip into a pan with the vinegar and gently bring to a very light simmer for about 5 mins. Allow to cool to room temperature, then strain through a muslin-lined, fine mesh sieve into a large, sterilised jar and seal with a lid.
Keep it in the fridge and serve topped up with fizzy or still water – add a sprig of fresh verbena or lemon balm if you like. Will keep in the fridge for up to 4 months.