Cook diced onions in butter and olive oil for a few minutes.

Add garlic and cook until fragrant and onions are translucent.

Add sliced zucchini, and season with vegetable stock.

Add salt to your liking and add in one liter of water.

Simmer for 20 minutes until the zucchini is soft.

Use your handheld immersion blender to turn your soup into a smooth purée.

If you want to freeze your soup. You can wait for it to cool down at this point and you can freeze.

Or you can add some yogurt to give it some creaminess and serve.