For the marinade, mix soy sauce, starch and sugar. Dab meat dry and cut lengthwise into strips. Place the meat in the prepared marinade, cover and chill.
In the meantime peel, wash and dice the sweet potatoes. Peel and finely dice the onions and garlic. Wash lime hot, grate dry, grate peel thinly, halve fruit and squeeze juice.
Wash and clean the chillies and cut into very thin rings.
Heat 1 tablespoon of oil. Fry the onion and garlic for about 5 minutes. Add potatoes, coconut milk and stock, bring to the boil and simmer for about 20 minutes. Season with lime juice and chili, except for a little bit for sprinkling.
Remove the meat from the marinade and put it on skewers one by one. Finely puree the soup and season to taste with salt and pepper. Heat 2 tablespoons of oil in a frying pan and fry the meat skewers in it in portions for about 2 minutes while turning.
Arrange soup and meat skewers. Sprinkle with chilli and lime peel and garnish with coriander.