Note, everyone who makes marmalade will have their own trusted method, and preferred flavour. This one works for me, and is thick, tangy and spicy.
It's probably not as frugal a jam as many others because traditionally it is made from Seville oranges, which are not the sort of fruit that you are likely to have a surplus of. However it is as much fun to do as to eat.
Step 1: Choosing the fruit
You can also add other types of oranges. This version used seven Seville oranges, three lemons and two grapefruit.