Chop the onion and garlic and sauté briefly in a little butter. Add the diced potatoes, sauté briefly, add the stock, bring to the boil and simmer on a low heat for 10-15 minutes. When the potatoes are done, add the sour cream and rocket leaves and mix the soup briefly. Add the white wine and the asparagus in thin slices and let the asparagus steep for a bit. Season to taste with salt, pepper and a little nutmeg.