Valencia Orange Marmalade

Directions

1. DAY 1: Place the lemon eighths in a nonreactive saucepan where they will fit snugly in a single layer. Add enough cold water for the fruit to bob freely. Cover tightly and let rest overnight at room temperature.
2. DAY 1: In a separate nonreactive saucepan, place the sliced oranges with water to reach 1 inch above the tops. Cover tightly and let rest overnight at room temperature.
3. DAY 2: Prepare the cooked lemon juice: Bring the pan with the lemon eighths to a boil over high heat, then reduce the heat to medium. Cook the fruit at a lively simmer, covered, for 2 to 3 hours, or until the lemons are very soft and the liquid has become slightly syrupy. As the lemons cook, press down on them gently with a spoon every 30 minutes or so, adding a little more water if necessary. The water level should stay consistently high enough for the fruit to remain well-submerged as it cooks.
4. DAY 2: When the lemons are finished cooking, strain their juice by pouring the hot fruit and liquid into a medium strainer or colander suspended over a heatproof storage container or nonreactive saucepan. Cover the entire setup well with plastic wrap and let drip overnight at room temperature.
5. DAY 2: Meanwhile, prepare the orange slices: Bring the pan with them to a boil over high heat, then decrease the heat to medium and cook, covered, at a lively simmer for 30 to 40 minutes, or until the fruit is very tender. If necessary, add a little more water during the cooking; the fruit should remain submerged throughout the cooking process. When the oranges have finished cooking, remove the pan from heat, cover tightly, and let rest overnight at room temperature.
6. DAY 3: Place a saucer with five metal teaspoons in a flat place in your freezer for testing the marmalade later.
7. DAY 3: Remove the plastic wrap from the lemon eighths and their juice and discard the lemons. Strain the juice through a very fine mesh strainer to remove any lingering solids.
8. DAY 3: In a large mixing bowl, combine the sugar, cooked lemon juice, fresh lemon juice, and orange slices and their liquid, stirring well. Transfer the mixture to an 11-quart copper preserving pan or a wide nonreactive kettle.
9. DAY 3: Bring the mixture to a boil over high heat. Cook at a rapid boil until the setting point is reached; this will take a minimum of 30 minutes, but may take longer, depending on your individual stove and pan. Initially, the mixture will bubble gently for several minutes; then, as more moisture cooks out of it and its sugar concentration increases, it will begin foaming. Do not stir it at all during the initial bubbling; then, once it starts to foam, stir it gently every few minutes with a heatproof rubber spatula. As it gets close to being done, stir it slowly every minute or two to prevent burning, decreasing the heat a tiny bit if necessary. The marmalade is ready for testing when its color darkens slightly and its bubbles become very small.
10. DAY 3: To test the marmalade for doneness, remove it from the heat and carefully transfer a small representative half-spoonful of marmalade onto one of your frozen spoons. It should look shiny, with tiny bubbles throughout. Replace the spoon in the freezer for 3 to 4 minutes, then remove and carefully feel the underside of the spoon. It should be neither warm nor cold; if still warm, return it to the freezer for a moment. Tilt the spoon vertically to see whether the marmalade runs; if it does not run, and if its top layer has thickened to a jelly consistency, it is done. If it runs, cook it for another few minutes, stirring, and test again, repeating more times if necessary.
11. DAY 3: When the marmalade has finished cooking, turn off the heat but do not stir. Using a stainless steel spoon, skim off any surface foam and discard. Pour the marmalade into sterilized jars, processing according to the manufacturer's instructions or another method of your choice.