1  onion, chopped
3 tablespoons mustard seeds
1/2 teaspoon red pepper flakes
2  garlic cloves
1 teaspoon peppercorns
1/2 teaspoon ginger
1  inch cinnamon bark
1 teaspoon whole cloves
1/2 teaspoon cardamom seeds
2 cups vinegar
1/2 cup molasses
1/2 cup soy sauce
1/4 cup tamarind pulp or 6 tablespoons lemon juice
3 tablespoons salt
1/4 teaspoon curry powder
1  anchovy, mashed
1/2 cup water
1/2 cup sugar

Tie first 9 ingredients loosely in a cloth. Simmer spice packet in a large heavy pan with next 5 ingredients. Mix curry powder, anchovy, and water in a cup and add to pan.

While spices are boiling, caramelize sugar by placing in a heavy skillet and stirring vigorously over a high heat. Move the sugar back and forth as it starts to melt and brown. Lower heat. Move sugar continuously, chopping at it to break the lumps until it becomes almost black and soupy, but not burned. Remove from heat.

Take the spice bag from sauce, squeeze, and carefully pour a little of the boiling spiced liquid into the sugar skillet, stirring briskly until dissolved. Return the liquid sugar to the large pan. Boil briefly. Pour into a bowl, replace the spice bag in the sauce, cool and let stand in the refrigerator, covered tightly for about 2 weeks. Stir from time to time and squeeze the bag. Bottle, keep refrigerated and shake well before using.