Spiced rhubarb ketchup

4 cups trimmed and chopped rhubarb (about 11⁄4 pounds);

1 cup chopped red onion;

1⁄4 cup golden raisins;

3⁄4 cup sugar;

1⁄2 cup organic unfiltered cider vinegar or white wine vinegar;

2 teaspoons finely grated orange zest;

Juice of 1 orange (about 1⁄2 cup);

1 tablespoon peeled and finely grated ginger;

1⁄2 teaspoon ground cinnamon;

1⁄8 teaspoon ground cloves;

1⁄2 teaspoon whole yellow mustard seed;

1⁄2 teaspoon kosher salt;

2 tablespoons ruby port.

Stir together the rhubarb, onion, raisins, sugar, vinegar, orange zest, orange juice, ginger, cinnamon, cloves, mustard seed, and salt in a large saucepan. Bring to a boil over medium-high heat. Remove the pan from the heat, cover, and set aside for 30 minutes.
Cook over medium heat until the rhubarb is very tender and the liquid is thick enough to coat the back of a spoon, about 10 minutes. Remove from the heat, stir in the port, and set aside to cool to room temperature.
Transfer into a clean glass jar, cover, and refrigerate until chilled. This keeps for up to 3 weeks.