I never seem to have much luck with jam made the traditional way on the stove with a preserving pan, it always seems to end in tears and a blackened pot. I went on a foraging course at Ballymaloe with Darina Allen and she explained that making just one or two jars was much easier than trying to fill your pantry with rows of preserves for a long winter ahead. You can also take advantage of reduced fruit at the supermarket and just use a couple of punnets.
So for foolproof strawberry jam I use 800 g (two punnets) or strawberries which had been sitting in the fridge for too long and looked a bit manky and 800 g of jam sugar (with pectin). I use a large stoneware pudding basin which is microwave safe, you need plenty of room as the jam rises when it boils more than you would think. So slice up the strawberries and cook on high for 7 minutes then mash up with a potato masher. Stir in the sugar until it disolves and then cook on high for 15 minutes. You can add a very small amount of butter with the sugar if you like to prevent the scum forming. Then remove and pot. The mixture needs to boil for at least 4 minutes to activate the pectin but these timings seem to work well - don't be tempted to peak or you will interrupt the boiling. Also boiling sugar is VERY HOT. Make sure your bowl is big enough to avoid your microwave turning into a sticky mess as you don't want this boiling over.
I've now got 3 jars of strawberry and 8 of blackcurrant as well as some redcurrant jelly from a few potterings around the kitchen. I used Delia's recipe for redcurrant jelly which just involves the above recipe but you strain it all through a nylon sieve before potting up. If you are very patient and don't rub the fruit through the sieve the jelly is clearer but it does seem a waste not to extract every last drop.
For the blackcurrants I use half jam sugar and half plain granulated. Now roll on the plums and blackberries which are looking wonderful this year despite the wasps and hornets.
