Instructions

1. 1

   Wash the mirabelles, leave them to drain and remove the stalks.

2. 2

   Halve the fruit along the seam and lift out the stones. The stones go in the bin and are never cooked with the fruit, because stone fruit kernels can release hydrocyanic acid.

3. 3

   Weigh the stoned flesh; if the mirabelles are very large, cut the halves again.

4. 4

   Squeeze the lemon. Slit the vanilla pod lengthways and scrape out the seeds with the back of the knife.

5. 5

   Mix the mirabelles, lemon juice, vanilla seeds and the 2:1 preserving sugar in a tall pan, cover and leave in a cool place until plenty of juice has been drawn out.

6. 6

   Sterilise four screw-top jars of 250 ml each and their matching lids in a large pan of vigorously boiling water, then lift them out with tongs and leave them to drain on a clean cloth. Only germ-free jars will keep the jam good for a long time.

7. 7

   Bring the mixture to the boil, stirring, then let it boil hard over full heat, stirring constantly and skimming off the foam. The preserving sugar only sets to work at a rolling boil.

8. 8

   If you like, blitz the hot mixture briefly and coarsely with a stick blender so that it spreads more easily.

9. 9

   For the set test, drop a blob onto a cold plate; if it firms up after a minute, the jam is ready. If it stays runny, boil for another minute and repeat the test.

10. 10

    Ladle the boiling hot jam straight into the prepared jars to about 1 cm below the rim, wipe the rims with a clean cloth and screw the lids on tightly at once.

11. 11

    The jars do not need to be turned upside down; simply stand them up and let them cool completely. As they cool, the lids pull inwards with an audible pop.