Rinse the fresh or defrosted goulash and dry it with paper towels. Chop large pieces into bite-sized pieces. Halve the onion lengthways, cap both ends, peel, halve the halves lengthways and cut across into approx. 5 mm thick slices. Cut the fresh, washed and peeled ginger crosswise into thin slices. Weigh frozen goods.
Wash the red peppers, quarter them lengthways, remove the stalks, grains and the white partitions. Cut the quarters lengthways into thirds and cut across into strips approx. 1 cm wide. Wash the small, green chillies and cut them crosswise into thin slices. Leave the grains and discard the stems. Wash the tomatoes, remove the stems, cut in half lengthways and remove the green stalk. Halve the halves lengthways and thirds across.
Heat a wok and add 3 tablespoons of the sunflower oil and let it get hot. Add the goulash in 2 portions and fry brown all over. Transfer to a Dutch oven with a slotted spoon. Add the rest of the sunflower oil and heat it up. Add the ingredients from onions to chillies and stir-fry until the onions are translucent. Add the tomato pieces and stir-fry for another 3 minutes. Deglaze with the tomato juice and simmer on reduced heat for 5 minutes with the lid on. Take off the stove and let cool down a bit.
In the meantime, wash the fresh lemongrass, remove the hard stalk at the bottom, remove the brown and withered leaves and only use the white to light green parts. Cut this into pieces approx. 8 cm long. Remove the outer, green leaves if necessary. Gently tap the lower half of the pieces with the back of the knife. The stems should remain optically intact. Wash the kaffir lime leaves and use them whole.
Pour the mixture from the wok into a blender and purée finely at high speed for 1 minute. Add the puree to the meat in the casserole. Add the spices and simmer with the lid on for 150 minutes. If the broth thickens too much, keep it liquid with a little water. Season to taste at the end.
Wash and peel the potatoes, cut in half lengthways, halves lengthways and quarter across. Cap the garlic cloves at both ends, peel and squeeze with a garlic press. Wash and roughly chop fresh celery leaves.
Add the potato pieces and simmer for another 20 minutes. Stir in the garlic 5 minutes before the end. Remove the cinnamon stick, lemongrass and kaffir lime leaves. Distribute the finished soup on the serving bowls, garnish, serve warm and enjoy.