Sweet, but with a balanced undernote of tartness from the citrus rind, this pretty red marmalade makes a lovely addition to breakfast or brunch.
Cut the oranges and grapefruit into 1-inch pieces, discarding the seeds but leaving the skin (rind) on. Place in the bowl of a food processor and pulse repeatedly until the mixture is finely chopped.
Transfer the chopped citrus to a heavy-bottomed saucepan and add the grated fresh ginger, 3 cups of water, and the sugar. Bring to a boil over high heat, stirring frequently. Once it has reached a boil, reduce the heat to maintain a very low simmer, cover the pan, and cook the mixture for 30 minutes. Watch the heat: if it's too high, the marmalade will boil over and make a mess of the stove!
After 30 minutes, remove the cover, and let the mixture cook until thickened, stirring frequently, about 10 to 15 minutes. Some syrupy liquid may be left in the mixture, but it will continue to thicken as it cools. Cool slightly, then add the minced crystallized ginger, stirring to combine.
Transfer the warm marmalade to a clean container or into sterilized glass jars. Keep refrigerated for up to 3 weeks, or follow the manufacturer's instructions on your canning bath for canning/preserving.