1. Rinse plums and tomatoes. Pit plums and cut into chunks. Core tomatoes and cut into chunks. In a blender or food processor, purée plums, tomatoes, and ginger.
2. In a 10- to 12-inch frying pan over high heat, combine purée, onion, brown sugar, soy sauce, and broth. Stir often until reduced to 1 1/2 cups, 15 to 18 minutes.
Nutritional analysis per tablespoon.