Stir all the time while cooking with a silicone spatula which does not melt or with a wooden spatula.
Put the empty jars and covers in the oven for 30 minutes at 100 °C (212°F) to sterilise them.
Once the jars are filled with jam, close them and turn them upside down to ensure they are hermetic and guarantee a long preservation.
The jam can be stored for one year approximately.