I made marmalade. I try to make marmalade every year, but you need Seville oranges to make it and they're only in the shops for about a week at the start of January. Sometimes not even that long, so I quite often miss out. This is in fact the worst time that I could possibly post a marmalade howto, given that nobody will be able to buy the ingredients, but whatever.
n kg of Seville oranges (They're really bitter and offset all the sugar. Normal oranges are too sweet)
2n kg of preserving sugar (It's got extra pectin in it, I used 2kg)
2n lemons (rounded down)
Put the oranges and lemons in a large, heavy bottomed pan and simmer them in 2 litres of boiling water for 2 hours, with a lid on. I used 2 litres of boiling water with 1kg of oranges, you may need to adjust. Make sure the oranges are covered. The point here is to make the oranges soft enough that you can scoop out the middle with a spoon, they'll be ready when you can easily push a butter knife into them.
Take the oranges out, keeping the water in the pan.
Let the oranges cool a bit, then halve them and scoop out the middle. Put all the goop from the middle into some muslin and then squeeze all the juice out into the water in the pan. If you don't have muslin, you can always just use a seive. Whatever gets you the juice and none of the white bits. Throw away the middle bits that are left.
Slice the skins, these are going to be the bits in the marmalade. They don't seem to change size much, so cut them up as you want them in the finished product. I used the whole lot.
Now, bring the water back to the boil and dissolve the sugar in it. Then tip in the peel.
You need to boil the mix rapidly for 20-25 minutes until it's at the setting point. This is the tricky bit. If you don't boil it long enough, you'll get very runny marmalade. Too much and you might burn it. The trick I use is to keep a plate cold in the fridge and when I think the marmalade is ready, drip some onto the plate and see if it starts to set and form a skin. It's never going to set as well as in the shops, but it'll taste a lot better.
Once it's done, let it cool. You'll get lots of skummy looking bubbles on top. I'd scoop these out so your marmalade is nice and clear.
Once it's cooled a bit, put it in some sterilised jars.