Don't double a jelly/jam/soft spread recipe. Apparently the ingredients don't cook the same and your final product will be liquid. Not a fun thing to find out after what seemed like marathon chopping. And processing. And waiting. For seemingly nothing.
BUT! I remembered that I have this book and although I've only ever glanced at it, it sure came in handy yesterday!!
It's quite helpful and full of tons of 'recipes'. Lucky for me there's a troubleshooting section and a cure for runny jelly!! It involves recooking all your previously processed jelly with more sugar, lemon juice (even if the original recipe didn't call for it) and pectin (there are separate cures for liquid or powder variety pectins).
Thankfully all my jars of jelly set up this time and I can enjoy some today! :p
I thoroughly recommend this book...there is so much info in it!!