Orange Marmalade (Irish)

Orange marmalade is associated above all with Scotland, and especially with the town of Dundee, where - according to folklore - an eighteenth-century merchant named James Keiller ended up with a cargo of bitter oranges instead of sweet ones, and passed them on to his obviously industrious wife, who turned them into what must have been very many jars of bittersweet preserves. In fact, the word marmalade, from the Portuguese marmelada, "quince paste," has been used to describe fruit preserves in English since at least 1480, and has referred specifically to citrus preserves since the seventeenth century.
Oranges, lemons, and other exotic fruits were being imported in considerable quantity into Ireland by then, and orange marmalade was almost certainly being made on the island, and in Scotland, before James Keiller was born. The addition of whiskey to marmalade is probably a more recent innovation.

2 lbs Seville or other bitter oranges, halved crosswise (1 kg)
8 cups sugar (1.5 kg)
3 Tbsp. Irish whiskey (optional)

Squeeze the juice from the oranges into a large nonreactive bowl. With a sharp spoon or grapefruit knife, scrape out and discard the flesh, seeds, and pith from the peels.

Cut the orange peels into thin strips no more than 2" (5 cm) long and add to the bowl with the juice. Add 4 cups (1 L) of water to the bowl and stir gently. Cover and refrigerate overnight.

Put the orange peels and liquid into a large nonreactive pot, and bring to a boil over high heat. Reduce the heat and simmer, uncovered, for 2-2½ hours or until the peel is soft enough to dissolve between your fingers and the liquid is reduced by about half.

Stir in the sugar a little at a time, making sure it is well dissolved. (If you add sugar before the orange peels are very soft, they will harden.) Increase the heat to medium-high and boil gently for 15-20 minutes, or until the temperature reaches 220°F/100°C on a candy thermometer, skimming any foam that rises to the surface. Reduce the heat and test to see if the marmalade has set by spooning a bit of the marmalade onto a chilled saucer. Allow the marmalade to cool slightly, then tilt the saucer to one side. If the marmalade remains in a blob with a few ripples, it's ready. If you wish to add whiskey, remove the pot from the heat and allow marmalade to cool for 10-15 minutes; then stir in the whiskey.

Divide the marmalade evenly between 6-8 sterilized (1 pt/475 mL jars); then seal with sterilized rings and lids. Transfer the filled jars to a canning rack, submerge in a pot of gently boiling water (make sure that jars are covered by at least 1" (2.5 cm) of water), and boil for 5 minutes. Carefully lift the jars from the water with jar tongs and place on a dish towel to cool, undisturbed, for 24 hours.

Makes enough to fill 6-8 (1 pt/475 mL jars).