Instructions

1. Weigh the oranges. For every 1 lb. of oranges, measure out 1 1⁄2 lbs. sugar and 2 cups cold water and set aside separately.
2. Thoroughly wash oranges in hot water to remove any wax film, then put into a large pot, cover with cold water (not the water you have set aside), and bring to a boil over high heat. Reduce heat to medium-low and simmer for 1 hour. Drain oranges and set aside until cool enough to handle.
3. Quarter oranges lengthwise. Working over a large sieve set over a large heavy-bottomed, nonreactive pot, firmly squeeze out seeds, juice, and most of the pulp from the oranges, setting peels aside. Transfer seeds and pulp to a 12" square of cheesecloth, gather corners together, and tie shut with kitchen twine. Add pouch to pot. Cut peels in half lengthwise, then thinly slice crosswise and add to pot.
4. Put the sugar and water you have set aside into the pot and bring to a boil over high heat, stirring often until sugar dissolves. Reduce heat to medium-low and simmer, stirring occasionally, until peels are very soft, liquid is deep golden, and temperature reaches 222° on a candy thermometer, about 2 hours. To check whether marmalade is thick enough to set, spoon about 1 tbsp. onto a small plate, transfer to the freezer for 2 minutes, then tilt plate; if jam "wrinkles", it's done. When done, firmly press pouch between two slotted spoons, releasing liquid into pot; discard pouch. Spoon hot marmalade into 4 hot, sterilized 12-oz. canning jars. Set lids on top and seal. Set jars aside to cool completely, then store in a cool, dark place for at least 2 months before serving (marmalade will keep, unopened, for up to 1 year).