Wash the fresh kailan, separate the leaves and flowers from the stem with an approx. 5 cm stem. Separate approx. 2 cm from the stem at the bottom. Peel the area down from the 3rd sheet. Separate the thin petioles from the leaves along the midrib, cutting the large leaves in half lengthways and crossways. Cut the leaf stalks into pieces approx. 2 cm long and cut the peeled stems crosswise into approx. 8 mm thick slices and keep them ready separately.
Wash the carrot, cap both ends, peel, halve lengthways and cut across into approx. 5 mm thick slices. Wash, peel and halve the sweet potato lengthways. Remove the wooden part (a kind of string) running in the middle. In some sweet potatoes, it is difficult to see when raw. Halve the halves and remove about 5 - 6 mm from the pointed part. Cut the quarters into bite-sized pieces. Wash, peel and finely grate the ginger. Squeeze the garlic.
Bring the water to the boil, dissolve the mushroom bouillon in it, add the potatoes and ginger and simmer for 23 minutes. After 10 minutes add the carrots. After another 5 minutes add the kailan stalks and leaf stalks. After another 5 minutes add the leaves, flowers and garlic and cook in 3 minutes to finish. Finally, season the broth to taste.
Distribute the finished soup on the serving bowls. Add the sesame oil and enjoy serving warm.