This is based on a really old recipe one of my Grandmother's friends used to use. I was never a fan of marmalade as a kid until I tried hers, and I wrote her 'reciept' down and kept it. I've messed with it a bit since then, and while I prefer the product which I get when I use Myer Lemons from my little potted tree on my back deck, this is almost as good using Eurekas or Ponderosas from the supermarket. Make sure you've got a candy thermometer around to use! I've found that the apple skin helps set the marmalade better; you can make it without the skin, but it will be a very loose, soft-set product.