In a pot with a thick bottom, melt butter with olive oil. Add onion cut into cubes and soften it. Add garlic pressed through a garlic press and sauté together a bit longer.
Add zucchini cut into cubes and sauté, stirring occasionally for about 2 minutes.
Pour with broth and bring to a boil. Season with salt, pepper and cook for about 25 minutes covered on medium heat. Blend the soup in an immersion blender into a cream, add cream at the end.
Serve with chives and garlic croutons or crumbled feta cheese.