Bring the stock or water to the boil in a large saucepan. Peel the potato, onion and carrots and cut into small chunks. Peel and quarter the garlic cloves.
When the stock is boiling, stir in the vegetables, garlic and some salt. Bring back to the boil, reduce the heat, partially cover and boil gently for 15–20 minutes.
Meanwhile, seed and finely chop the chilli, peel and finely chop the ginger, and squeeze the juice from the lemon or lime.
Heat the olive oil in a small pan and fry the chilli and ginger for about 1 minute, but do not let them burn. Stir in the garam masala, five-spice powder or mixed spice and the juice; cook for 1 minute.
Add the sesame seed oil and stir over the heat until the mixture thickens. Remove the pan from the heat and put aside.
When the vegetables are tender, stir in the ginger sauce, then process or blend the mixture into a smooth purée. Return the purée to the pan, season with black pepper to taste, then reheat and serve with the garnish of your choice.