The recipe is easy: chop up lemons finely. I used Meyer lemons, available only from November to early January. Remove as many seeds/pips as possible, as well as the thick membrane that runs down the center of the fruit. This is the messiest part of the job!
Measure the chopped fruit into a heavy saucepan and add the same amount of water. For example, if you get 3 cups of chopped fruit, add 3 cups of water. Bring mixture to a hard boil and cook for 25 to 30 minutes until peels are soft. Remove from heat. Measure out a like amount of sugar ... again, if you got three cups of chopped fruit, measure out three cups of sugar. Add sugar to pan and return to heat. Cook over high heat, stirring frequently, until the marmalade thickens and sheets off the spoon instead of drips. If you use a thermometer, this can be around 217 - 222 degrees Fahrenheit. Remove from heat immediately and spoon marmalade into clean jars. Refrigerate.
Now before you yell at me for not sterilizing my jars ... I get roughly four jars of marmalade from five lemons, all of which will be devoured by next week. Lemons are extremely acidic, which means they're a poor host for botulism, and I store my jars in the refrigerator. If you plan to give your marmalade away or store it for awhile, then I would advise you to consult with a proper preserve-making handbook.
Enjoy the fruits of January!