Turn jars upside down for a few minutes so there are no air bubbles and the rim is sterilized.

Turn jars right side up again and allow to cool.

Optional: sterilize jars in a water bath for longer shelf life.

Remove stems and cores/seeds and cut into pieces.

Press fruit through a fine sieve to remove small seeds (optional for berries).

Place fruit in a tall pot, slowly sprinkle in jam sugar, and stir vigorously.

Bring to a rolling boil while stirring occasionally.

Place 1 tsp of the boiling fruit mixture onto a cold plate and check after a few minutes whether the mixture sets.

If the wrinkle test is negative, add a little citric acid and test again.

Ladle into jars to just below the rim.

Wipe splashes from the rim with a clean cloth and seal the lid tightly.