Add the gooseberries, measurement water and rosemary to a preserving pan. Bring to the boil, then cover and simmer gently for 20–30 minutes, stirring and mashing the fruit from time to time with a fork, until soft.
Leave to cool slightly, then pour into a scalded jelly bag suspended over a large bowl and allow to drip for several hours.
Measure the clear liquid and pour back into the rinsed preserving pan. Weigh 500 g (1 lb) sugar for every 600 ml (1 pint) of liquid, then pour into the preserving pan. Heat gently, stirring from to time, until the sugar has dissolved.
Bring to the boil, then boil rapidly until setting point is reached (10–15 minutes). Skim with a draining spoon or stir in butter if needed.
Ladle into warm, dry jars, filling to the very top. Cover with screw-top lids, or with waxed discs and cellophane tops secured with elastic bands. Label and leave to cool.
To serve, try this jelly with grilled herrings and salad.