A marmalade is a preserve that includes the rind of the fruit. The original marmalade was not made with oranges, but quince, and the name marmalade comes from the Portuguese word for for quince jam. History lesson over.
Cooking lesson begins. Orange marmalade is most often made with Seville oranges, which are less sweet than other varieties. If you cannot get Sevilles, substitute a lemon for one orange in every pound of oranges you use.
One recipe calls for you to cut and seed 2 pounds of oranges, squeeze out the juice, remove the membranes and ends of the orange, and then cut the remaining peels into thin strips. Put the peels and juice into a pan. Chop a large lemon and tie it up along with the orange membranes, ends, and seeds in a cheesecloth bag, which you also toss in the pan. Add 9 cups of water and simmer the mixture for at least two hours, until the peels are very soft.
Remove the lemon bag, and squeeze all the juices into the pan (with tongs, not fingers). Add 9 cups of sugar and stir over low heat until it is dissolved completely. Increase the heat and boil rapidly for 15 to 20 minutes, without stirring. Skim off any scum from the surface. The recipe makes about 11 cups of marmalade.