Melt the butter in a heavy pot over medium heat. When it foams, add the garlic and onions and cook on medium-low heat for about 10 minutes, or until the onion is soft and translucent.
When the onions are soft, add the zucchini and cook until soft.
Add enough broth to cover the vegetables and bring to a simmer, simmering at low heat for about 45 minutes.
Let cool slightly, then blend with an immersion blender or transfer to a standing blender to puree.
Taste and season with ginger, salt, and pepper. Serve with a drizzle of olive oil and some croutons, if you have them on hand.
