This is one of my favorite marmalades. Soaking the sliced oranges overnight makes the rind soft and tender. I make this marmalade not only for buttered toast , but to use in sauces, cakes and crepes. —Sunnycovechef
Wash the oranges and lemons thoroughly. Cut both ends of the oranges and lemons, and discard. Working on a large plate to catch the juice, cut oranges and lemons in half lengthwise, then cut the halves into very thin slices crosswise. Discard most of the seeds, but leave some in for flavor. Put the fruit in a noncorrosive container, cover with four cups of water and let it stand covered for 24 hours.
Put everything in a large pot and simmer covered for one hour. Add the sugar, stirring and bring to a boil. Boil for about one hour, stirring occasionally to prevent sticking to bottom. Test for readiness by putting a teaspoon of jam on a small plate that has been in the freezer. If it gels, the marmalade is done. The mixture should be a soft gel. If it runs, it is not ready.
Meanwhile, in a large pot put the clean jars and bands in boiling water and boil for 10 minutes. Turn off the heat, add the lids and leave everything in the water until the marmalade is ready. I often run my jars through a cycle in the dishwasher and keep them warm in the dishwasher, so I don't have to put them in boiling water. However, it is important to be safe and follow the guidelines given by the US Department of Agriculture.
Ladle the jam into jars, leaving some space at the top. Wipe the top of the jar clean with a moist paper towel and add the lid. Screw the ring onto the jar. I turn the hot jars upside down for 20-30 minutes. After that, I check to make sure that they are sealed. If they are not, I put them in a water bath for 10-15 minutes and boil them until the tops pop. Place a jar rack, or metal mush basket in the pot to prevent the jars from touching the bottom. I use an old pie tin turned upside down. Fill the pot with water (halfway up the jars ). You know your jars are sealed when the lid doesn't move or pop when you press on it. To be totally safe, follow the manufacturer's instructions that comes with the jars.