Ingredients:

  • 2 tablespoons (30 g) unsalted butter OR 2 tablespoons (30 ml) extra-virgin olive oil (for vegan)
  • 4 medium yellow onions, thinly sliced (about 600 g / 1.3 lb)
  • 8 oz (225 g) pitted prunes, roughly chopped
  • 1/3 cup (70 g) packed dark brown sugar (or maple syrup/honey for variation)
  • 1/4 cup (60 ml) good balsamic vinegar
  • 1/4 cup (60 ml) port or dry red wine (optional; use extra water/stock if omitting)
  • 1 tablespoon (15 ml) fresh lemon juice (or 1.5 teaspoons / 7 g lemon juice concentrate)
  • 1 tablespoon fresh thyme leaves (or 1 teaspoon dried thyme)
  • 1 teaspoon kosher salt (about 5 g) — adjust to taste
  • 1/2 teaspoon freshly ground black pepper
  • 1/4 teaspoon crushed red pepper flakes (optional, for heat)
  • 1/4 to 1/2 cup (60–120 ml) water or low-sodium chicken/vegetable stock (as needed to loosen)
  • Optional finishing/garnish: 1 teaspoon whole mustard seeds, toasted
  • Optional finishing/garnish: 1 tablespoon finely chopped fresh parsley or additional thyme

Instructions:

  1. Prep: Slice onions thinly, roughly chop pitted prunes, and measure remaining ingredients. If desired, warm the pan briefly before cooking.
  2. Caramelize onions: Heat a large heavy-bottomed skillet over medium-low and add butter or olive oil. Add sliced onions with a pinch of salt and cook low and slow, stirring every few minutes. After about 10–12 minutes they will be limp and pale golden; continue another 10–20 minutes until deep golden-brown and jammy, adjusting heat to avoid burning.
  3. Build the jam: If the pan is dry, add 1–2 tablespoons water and scrape up browned bits. Add chopped prunes, brown sugar (or maple/honey), thyme, mustard seeds (if using) and crushed red pepper flakes, and stir to combine for 1–2 minutes.
  4. Deglaze and simmer: Pour in port or red wine (or water/stock) and balsamic vinegar, bring to a gentle simmer, then reduce heat to low. Simmer uncovered for 15–25 minutes, stirring occasionally, until the mixture is thick, glossy and the prunes are soft and partially broken down. Add water or stock a tablespoon at a time if too dry to reach a spreadable jam consistency.
  5. Finish and adjust: Stir in lemon juice and taste; adjust salt, sugar or acid to balance sweet and tart. For a smoother texture, pulse with an immersion blender or process a portion in a food processor (use caution with hot mixture).
  6. Cool and store: Let cool slightly, transfer to sterilized jars or airtight containers, refrigerate up to 2 weeks or freeze up to 3 months. For shelf-stable canning, follow tested water-bath canning procedures (not covered here).