Heat the oil in a soup pot or Dutch oven. Add the curry powder and turmeric, then stir in the onion and sauté over medium heat. After five minutes, add the ginger, potato and carrot. Stir.
When the carrots are soft enough to break easily with a wooden spoon, remove the pan from heat and stir in the peanut butter. Let cool for 5 minutes. Pour the carrots into a food processor or blender and whiz until smooth (at high speed for several minutes). Add the coconut milk, lime juice, and orange juice, and whiz again. If the mixture is too thick, add more stock or orange juice or a combination of the two.
If necessary, heat the mixture in the same pan briefly before serving. Pour a stream of the extra coconut milk into the top of the soup after filling bowls. Garnish with mint leaves, or coriander (cilantro) or chives, depending on your taste.