Place broth in a cook pan over medium heat. Cook onions in the broth until just softened, about 3-5 minutes. Add garlic and ginger and continue cooking for 3 more minutes
Reduce heat to low and add remaining ingredients, simmering for about 5 minutes.
Cool mixture slightly and, using an immersion blender, high-speed mixer or food processor, blend until smooth.
Store in an airtight container in the refrigerator for up to two weeks.