Peel and finely chop the onion. Wash, clean and chop 3 zucchini. Grate the rest of the zucchini roughly. Heat 20 g fat in a pot and fry the onion in it. Add the zucchini pieces and fry for 8-10 minutes.
Season with salt and pepper. Deglaze with stock and cream and bring to the boil. Wash basil, dab dry and, except for a few leaves for garnishing, chop finely and add to the soup. Puree into the zucchini cream soup with a blender.
Add the zucchini rasp and cook over low heat for another 3-4 minutes. In the meantime, remove the crusts from the bread and cut into triangles. Peel garlic and cut into slices. Heat remaining butter in a pan.
Fry the chunks of bread and garlic until golden brown. Season the zucchini cream soup again and serve with the croutons. Serve garnished with the remaining basil.