Peel and finely dice the scallion. Heat the butter in a stock pot and stew scallion until glazed. Peel and wash the potatoes, cut into small cubes and add to the pot.
Wash the basil and set aside a few pretty leaves for decoration. Chop the remaining basil roughly and add to the potatoes. Fill vegetable stock into the pot, bring to boil slowly and let it simmer for 15 minutes. Take the soup from the hot plate and add the Silken Tofu. Purée in blender and drain through a fine strainer. Season the soup with salt and pepper and boil briefly once more. Season with lemon juice.
Divide soup onto 4 plates, garnish with basil leaves and enjoy while still hot.