Divide and cut the first batch: Divide the citrus in half by weight. Cut the first half coarsely into eighths and leave the seeds in. This batch is only here to give up its pectin and will be strained out later, so it does not need to look neat. If you are using lemons to balance sweet citrus, use the lemons for this first batch.

Soak overnight: Place the cut fruit in a nonreactive pot and add enough cold water to cover by about an inch. Cover the pot and let it rest overnight at room temperature to soften the peel and start releasing pectin.

Cook the first batch: Bring the soaked first batch to a boil over high heat, then reduce to a simmer. Cover and cook for 30 to 40 minutes, until the fruit is very soft and the liquid looks slightly syrupy. Add water as needed to keep the fruit submerged.

Strain and reserve the liquid: Strain the cooked fruit through a fine mesh sieve set over a clean nonreactive pot, pressing firmly on the solids to extract all of the pectin-rich liquid. Keep that reserved liquid, since it carries the pectin that will set your marmalade. You should end up with around 4 cups. Discard the spent chunks and seeds.

Prepare the slices: While the first batch cooks, thinly slice the remaining citrus, removing all of the seeds, since these slices stay in the finished marmalade. Cover the slices with water, bring to a boil, and boil for 5 minutes, then drain. For bitter citrus, repeat the boil with fresh water; for sweet citrus, skip the second boil.

Soak the slices overnight: Return the slices to the pot, cover with fresh water, bring to a boil, and simmer until tender. Remove from heat and let the slices cool and soak in their liquid overnight to soften further and release more pectin.

Get ready to finish: Place a saucer with several metal teaspoons in the freezer for testing the set. If canning, prepare a water bath canner and jars. Work in a pot large enough that the filling comes only about halfway up the sides, since marmalade foams as it cooks.

Combine everything: In the wide preserving pot, combine the reserved liquid from the first batch, the sliced fruit along with its soaking liquid, the lemon juice, and the sugar. Stir gently to dissolve the sugar without breaking up the slices. Do not leave out the reserved liquid or the lemon juice, as both go in now.

Cook to the setting point: Bring the mixture to a rapid boil over high heat and cook hard until it reaches the setting point, about 220 degrees F at sea level. This takes roughly 30 to 45 minutes. Let it bubble undisturbed at first, then stir gently every few minutes once it foams. Test with a frozen spoon or cold plate: a spoonful should wrinkle and hold its shape rather than run.