Some recipes call for the whole fruit to be thinly sliced and soaked, others require the whole fruit to be simmered for hours until tender, then chopped. In any case, the fruit is used in its entirety - peel, pith, seeds, juice and pulp.
You can use any type of citrus fruit. Should you be lucky enough to come across Seville oranges - they're slightly flatter than other oranges, with a sour, intensely orange flavour - nab them, because they're the ultimate marmalade-making fruit.
You'll need at least one lemon in the mix too: lemons are high in pectin and acid, both necessary for a well-set jam or marmalade. The acid activates the pectin which then sets the marmalade. Choose slightly under-ripe fruit for their higher pectin content, and avoid those with blemished skins. Soaking the fruit overnight helps release the pectin, while simmering the seeds and pith (tied up in a piece of muslin) in the mixture also aids the setting.
Recipes such as the one here require the peel to be removed from the fruit and sliced before cooking. Regardless of how the fruit is prepared, it's always simmered until tender before the sugar is added. Warming the sugar in the oven helps it to dissolve quickly when it's added to the marmalade.
When you're making jam or marmalade, it's essential to sterilise the vessels you intend to store it in. Glass jars are ideal, and there's no need to go out and buy them if you plan ahead a little and save empty jars and lids from your pantry. Soak them, scrub off the labels and put them aside for a rainy day's preserving. When that rainy day arrives, you'll need to sterilise the jars and lids, either by running them through the rinse cycle of the dishwasher, or by hand-washing them, placing them upright on an oven tray in a cold oven and turning the oven to 120C. Leave them in the oven for half an hour and you're good to go.
Selecting the right pan for the job is equally important. A heavy-based large, wide pan is preferable, giving the mixture ample room to reach a rolling boil and reach setting point quickly, thus preserving the fresh flavour of the citrus. Setting point is when the mixture reaches a firm set but doesn't veer into toffee territory. The time this takes will differ from batch to batch because of varying levels of pectin in the fruit. As the mixture bubbles and boils, it'll turn from a liquid into a syrup, and will darken in colour. The best way to test for setting point is on a chilled saucer (pop a couple into the freezer before you start cooking). Remove the pan from the heat, spoon a little mixture onto the chilled saucer and return it to the freezer for 30 seconds or so, then draw your finger through the mixture - it should leave a trail, indicating that the mixture has reached setting point. If not, return the pan to the heat and cook for another few minutes before testing again. If you prefer, use a sugar thermometer to measure when the mixture reaches 105C; once it does, you can begin testing for setting point.
Once setting point is reached, remove the marmalade from the heat and let it stand for 30 minutes, allowing it to thicken. Stir the marmalade to disperse the peel evenly, then ladle it into your sterilised jars. A jam funnel (a metal funnel with a wide neck) comes in handy at this stage, helping to avoid nasty burns. Seal, wipe away any spills with a hot wet cloth, cool to room temperature and label. Store the marmalade in a cool, dry, dark place for up to 12 months (once opened, store it in the refrigerator); try it in our marmalade and almond tart recipe.