Traditionally, marmalade is made with Seville oranges— which occasionally show up in season in the Bay Area for a week or two.
No added pectin– the pith copious number of seeds in a bitter orange produces enough (boiled in a muslin bag for ease of removal, in a pot with the whole rest of the orange sliced thin).
As the sugar heats, it bubbles up and changes form several times. In absence of a thermometer, dropping bits of marmalade on a chilled plate in a freezer until it forms a skin gives a hint it’s at the right stage. A splash of scotch whiskey in honor of The Bard‘s birthday adds a little smoke.
After canning, trying it out the next day. Tart and bitter and jelled– not bad!