It is important to use firm-fleshed plums for this recipe such as omega, black doris or prune plums. Juicy plums will be too watery and not thicken well. Apricots would also work well in this recipe. The addition of the apple adds pectin to help set the jam.
Ingredients
1kgomega plumsstones removed and cut into small pieces
1applecored with skin on and chopped into small pieces
1cupapple syrup or 3/4 cup honey
Instructions
Combine the plums, apples, and syrup in a heavy-based saucepan and bring to a gentle simmer. Cook, uncovered, on low heat for about 1 1/2 - 2 hours until thickened. Stir occasionally then more frequently as it thickens so it doesn't burn. Once the jam is lovely and syrupy [it will thicken some once it cools] spoon the hot jam into 4 or 5 hot sterilised jars.
Leave the jars to cool then check the lids are vacuum sealed. Store in a cool dark pantry and use within 6 months. Once opened keep refrigerated and use within a month.