Step 1

Preheat oven to 100C.

Step 2

Pick through fruit, remove stalks, leaves and bad raspberries.

Step 3

Squeeze juice of half a lemon into a small bowl. Reserve the juiced half.

Step 4

To sterlise the jars, wash jars and metal lids in hot, soapy water until spotless. Place jars and lids on a baking tray that allows some space between them. Heat in the oven for 25 minutes. Place lids in a pan of water and bring to the boil. Simmer for five minutes. Place on a clean rack to dry.

Step 5

Place the raspberries in your largest heavy-based pan (or, if you have one, nan's old wide-mouthed copper jam-making pan). Make sure it is spotless.

Step 6

Add sugar and lemon juice, place on high heat and start stirring with a long-handled wooden spoon. Ensure the mixture never stays in contact with the pan's bottom or edges too long. Do not burn the jam. The fruit will break down and release its juice. The sugar will dissolve. Add the juiced lemon half.

Step 7

Bring to the boil, stirring all the time. Keep jam at a rolling boiling but not so overheated that it foams out of the pan. Then remove the lemon half.

Step 8

After about 15 minutes you'll notice the jam starts to smell a little cooked, and that it resists your wooden spoon as the liquid evaporates.

Step 9

Watch how the jam behaves on the edge of your wooden spoon. Early on, it will run cleanly off. As it gets to the perfect setting point the mix will roll down slowly, form little dollops and look a bit jellified. If so, it's done.

Step 10

Carefully ladle the jam into the jars to fill just past shoulders. Screw on lids. Wipe cooled jars clean.