Georgian Pickled Plum Sauce (Tkemali)

Fill a large saucepan half full of water and bring to a boil over medium-high heat. Immerse the plums in the water for 1 minute, then drain and rinse under cold running water. Slip off the skins, using a sharp paring knife. Cut each plum around its circumference all the way to the stone, then twist the halves in opposite directions to separate them. Use a spoon to pop out the stone. Cut each plum half in half again.

Combine the plums, water, 3 tablespoons lemon juice, the oil, garlic, coriander, 1/2 teaspoon salt, and 1/2 teaspoon hot pepper flakes in a small nonreactive saucepan and bring to a boil over medium heat. Reduce the heat to low and simmer, covered, until the plums are very soft, about 5 minutes.

Transfer the mixture to a food processor or blender and process to a smooth purée. Return the purée to the saucepan and stir in the cilantro. Bring to a boil over medium heat, then reduce the heat to medium-low and simmer until the sauce is reduced to about 2 cups, about 5 minutes.

Remove from the heat and taste for seasoning, adding salt, pepper flakes, or lemon juice as necessary; the sauce should be highly seasoned. Cool to room temperature and serve at once, or store, tightly covered in the refrigerator, for up to 2 weeks.

Note: Prepare rhubarb as described above in step 2, substituting 1 pound fresh rhubarb, trimmed and diced, for the plums. You may need a tablespoon or so more sugar to balance the rhubarb's acidity.