In France, there is a legal distinction between a confiture and a conserve. The former has more sugar and is referred to in the UK as jam. A conserve contains a higher proportion of fruit, which has the advantage of extra flavour, but it is also more susceptible to spoilage. Properly made, it will keep for months in sterilised jars but once a jar is open, the contents need eating straightaway.
1.4kg preserving sugar
3 untreated lemons
Trim the ends of the rhubarb stalks. Cut into 25mm lengths. Layer the strawberries, rhubarb and preserving sugar in a mixing bowl and refrigerate overnight.
Line a bowl with a sheet of muslin. Chop the lemons coarsely. Put the pieces in muslin and tie up with kitchen string.
Empty the fruit and sugar into a stainless-steel pan. Put the bag of lemon on top. Bring to the boil over a rapid heat. It's better not to stir. Boil for 15 minutes before testing for setting point with a sugar boiling thermometer: 104-105ºC should give a light setting texture.
Take the jam off the heat. Remove any scum with a ladle or large spoon.
Pour or ladle the jam into hot, sterilised jars. Tap the jars on the work surface to prevent any air pockets forming. Fill to the rim and seal the jar.
Note on stirring: it prevents sticking, especially in pans with hot spots. With smaller quantities, stirring should be minimal but it is necessary with larger batches. Try to avoid splashing jam on to the sides of the pan since they can overcook and mar the flavour.
Photo © Tom Stockhill