Peel and chop the onion. Cut the carrots into thin slices and the celery into small cubes. Sauté the onion in oil until soft. Add the carrots and celery and sauté briefly. Pour in the vegetable soup, season with lovage and nutmeg. Simmer for 10 minutes, puree with a hand blender and keep warm. Wash the courgette and cut into very small cubes, finely slice the basil leaves. Heat the oil in a pan and fry the garlic briefly. Add the courgettes, fry briefly while stirring, season lightly with salt and remove from the pan. Stir in the basil.
Serve the soup in portions, sprinkle with courgette and garnish with basil.