Thaw the prawns. Dice the onion, cut the carrots and leek into strips as thin as possible.
Heat the oil in a soup pot and briefly sauté the onion cubes with the red curry paste. Add the carrots, the leek, a pinch of salt, the coconut milk and the stock (add 4 kaffir lime leaves from the Asian shop if you like) and simmer for about 8 minutes.
Add the prawns and simmer for another 5 minutes. Season to taste with the lime juice and the spices.
If you like it a little hotter, you can add chilli flakes.