Thanks to all the people who have posted bitter marmalade recipes online.  I chose this one because it seems to use the least amount of sugar and is a very simple recipe.  Strictly speaking it does not fit into my paradigm of low-carb foods and I probably won't include it in my recipe book.  And it fulfils the request from Rachael.  Enjoy!

Acknowledgements to Amy for this posting.

Bitter Orange Marmalade
(more a formula than a recipe)

Ripe or unripe oranges
Sugar

Wash and dry the fruit. Cut unpeeled into quarters lengthwise then slice very thin crosswise. Measure fruit, place in a large pot and add twice as much water. Let stand overnight.

The next day, bring to boil covered then uncover and simmer 1 hour. Let stand 24 hours.

Measure the fruit and liquid and add no more than 1 1/2 cups of sugar per 2 cups of fruit mixture. Boil until it reaches the consistency you like, probably between 10 and 20 minutes or so, it will thicken slightly as it cools.

Sterilize jars in whichever method you prefer. (I wash them with soapy water then fill them halfway with water and microwave for about 5 minutes, until the water boils, remove with potholders and empty them just before filling.) Pour marmalade into hot jars and seal. If your jars do not seal airtight, just keep the conserve in the refrigerator.

http://cookingwithamy.blogspot.com/2008/01/bitter-orange-marmalade-recipe.html