A patient of mine, a distant Chivers relative, gave me his three-day recipe which I have always diligently followed. However since some of the people I love do not like large peel slices I use the Cuisinart rather than a knife to chop the peel more finely and skip tradition. Because I was early, my oranges are plump and clean without scars. Sevilles, even so , are the most ugly of the orange varieties so don't be dissuaded by their lack of beauty! Don't take offence at the bitterness of the fruit. Ugly and bitter will transform to sublime in the hands of the lover. Gentle patience is all that is necessary. The following is the recipe I was given a la Chivers.
Day1, 8 large Seville oranges, 2 lemons. Halve these all and remove the fruit. Leave all the pith on the peel. Place the fruit in a muslin bag. Chop up the orange and lemon peel with the pith. (I use the Cuisinart). Place all the material together in a large container. {Make sure your muslin bag doesn't leak or you'll have seeds in your marmalade}. Add ten cups of water and soak overnight.
Day 2, Boil contents for 45 minutes. Let cool and rest for the balance of the day. I have found that you may need a little more water. Keep a sharp eye.
Day 3, Take out the muslin bag and squeeze well. Add one and one quarter cups of sugar to each cup of your product. Boil for 45 minutes timed from the point of rapid boiling. Simmer longer if the marmalade does not jell well when dripping off the spoon. Then fill your jars with hot product, the jars preheated at 275 degrees on a tray in the oven. Seal.
The quality of the jelling varies with the thickness of the pith in my view. The need to add water at any point varies with the varied hydration of the oranges. The marmalade darkens over the year but the quality is unchanged. No extra pectin is needed: no treacle: no food additives: just sugar and fruit. Bon appetite.