Neither long simmering nor heat-canned, this vibrant, lightly spiced jam couldn't be simpler to prepare. Red-fleshed plums lend a gorgeous garnet color, but any variety works well.
Bring plums and 1 cup water to a boil in a medium saucepan, then reduce heat to low and simmer until plums begin to soften and liquid is reduced by about half, about 5 minutes.
Meanwhile, finely grate ginger, then squeeze juice into a small bowl; discard pulp.
Combine sugar and pectin in a large bowl. Add plum mixture, lemon juice, pepper, cardamom, and 1 tsp. ginger juice (discard any remaining juice), then stir constantly for about 3 minutes to activate pectin. Using a potato masher or fork, break up any large plum pieces, then let cool at least 30 minutes.
Ladle jam into sterilized jars, leaving 1/2" from the top to allow for expansion. Cover and chill.
Jam can be made and chilled for up to 2 weeks or frozen for up to 1 year.
