Put a small plate in the freezer. Put the
rhubarb into a preserving pan or your largest
saucepan with the sugar and halved
vanilla pods. Heat gently, stirring, until all
the sugar has dissolved, then squeeze
in the lemon juice and increase the heat.
Boil for about 10 mins, skimming off the
scum as you go (the fruit should be soft).
Test for setting point by spooning a little
onto your chilled plate. After 1-2 mins,
push your finger through the jam – if the
surface wrinkles it is ready, if not, keep
cooking for 2-min intervals, testing in
between. (Or if you have a sugar
thermometer it should reach 105C)
Once the jam is ready, let it cool for
about 15 mins before ladling into warm
sterilised jars and sealing. Will keep for
6 months in a cool, dark place.