Melt the butter in a heavy 4-quart pot over medium heat. When it foams, add the sliced garlic and onions and cook on medium-low heat for about 10 minutes, or until the onion is soft and translucent. Keep the heat low enough that the garlic doesnt brown; you want everything to sweat.

When the onions are soft, add the zucchini and cook until soft. Add the broth and bring to a simmer. Simmer at a low heat for about 45 minutes.

Let cool slightly, then blend with an immersion blender until creamy, or transfer to a standing blender to puree. Be very careful if you use the latter; only fill the blender half full with each batch, and hold the lid down tightly with a towel.

Taste and season with ginger, salt and pepper. Like most soups, this is significantly better after a night in the refrigerator to let the flavors meld.