Step 1 Peel and core the apple, then coarsely chop. Coarsely chop the onion. Set aside.
Step 2 In a medium saucepan, combine the granulated and brown sugars, vinegar, orange zest, ginger, salt and cinnamon. Bring to a boil. Reduce the heat to low and add the apple, onion, blueberries and currants. Simmer, uncovered, until thick, 30 to 40 minutes, stirring occasionally. Cool to room temperature, about 30 minutes, before serving. (This can be made a week in advance and kept in the refrigerator.)
Step 3Makes 3 cups.