Thickening: if you have lemons, peel one after scraping the outer skin off and peel the pith, in strips, (the white matter) and put that in your jam or jelly. Remove it once it has finished cooking.

The fruit also makes a great chutney - if you like spicy, then add some cayene pepper or chili (to taste) Great thing about chutney is that you do not only eat it with curry and rice - it goes beautifully with all kinds of dishes. Only problem is - you would then have to plant more cacti...