Cut the ginger in many smallish pieces and put in a blender container with the garlic and vinegar. Blend 30 seconds.
Add miso and blend again for a few seconds. Pour the vegetable oil slowly into the blender as it is running. Keep the blender running as you add sesame oil, then water, and blend 30 seconds more.
Makes 2 cups. Good on roasted or grilled vegetables served hot or cold, on grilled fish, on green salad. You may also brush it on foods that are about to be grilled.