1 kg plums, stoned and quartered
250 g fresh blackberries, washed and stems removed
1 kg sugar
juice of 1 lemon
1 thin slice butter
- Before you start, put a saucer or plate into the freezer. You'll also need to sterilise 6 x 375ml jam jars (see tips, below).
- Throw all the ingredients except the butter into a heavy-based saucepan, mix around and bring to the boil.
- Once it has come to the boil, turn the heat down so it’s on a slow simmer for about 20-25 minutes. You will notice that there is a kind of froth that appears – don’t worry about it too much at this stage... we deal with that a little later on.
- To check if it’s ready take a dollop of jam and place it onto the frozen plate. You are looking to see if it sets. You can also streak your finger through the jam as well. If you notice a kind of ‘skin’ forming on the top, then you’ll know you are done – this is called the 'wrinkle test'.
- Now to deal with that froth! Take a thin slice from a block of butter and add it into the simmering jam. Stir it through for about a minute and the froth should disappear. If you still have some remaining, you could scoop it out.
- Ladle the hot jam into the warm, sterilised jars. Put the lids on immediately for a good seal.