For the yogurt soup, clean, wash and chop the leeks. Peel and crush the garlic. Bring water to a boil and crumble in vegetable soup cubes.
Melt butter in a saucepan and sauté garlic and leeks in it. Deglaze with balsamic vinegar and pour in vegetable soup. Season with salt and pepper and boil for another 3 minutes.
Remove from heat and puree. Stir in yogurt and drizzle in lemon juice. Chop chives and stir into yogurt soup as well before serving.