Before you start see Notes section below.
Put the raspberries, sugar and lemon juice into a preserving pan or similar.
Place pan over a gentle heat, stirring occasionally, until all the sugar crystals have dissolved. You can usually tell by running a wooden spoon over the bottom of the pan.
Bring the pan to a rolling boil and time for 7 minutes. Alternatively, if you have a jam/digital thermometer, boil until a temperature of 104.5℃ (220.1℉) is reached.
Take the pan off the heat and place a few drops of jam onto a chilled saucer and refrigerate for a minute.
Test the set by running your finger through the jam. If it forms a crinkle and is gel-like then the jam is ready to pot up.
If the jam isn’t ready continue boiling for another 2 minutes at a time and re-test until ready (mine took 9 minutes).
If there is froth (scum) on the surface of the jam mix it vigorously with a wooden spoon to eradicate.
Use a ladle and jam funnel to pot up the jam in sterilised jars and seal with lids immediately – makes 2 x 0.5 L (10 ounce) jars or variations there of (900 mls in total).
Once cool store in a cool, dry, dark place and refrigerate on opening.