I get a few gooseberries, about 2 oz to 2 lb of strawberries and chop the gooseberries up really small and just make the jam as usual with equal sugar to fruit. It sets every time and you can't taste the gooseberries.

What a good idea. I made some strawberry jam a fortnight ago and, though it appears set when you first open it, it becomes increasingly runny as the jam goes down in the jar. I did use lemon juice and sugar with pectin but it still didn't set properly, obviously. Next year I shall try the gooseberry trick, Plumpudding!