Wash and peel the cucumber and cut it in half lengthwise. Remove the seeds with a teaspoon. Cut the fruit flesh into bite-sized pieces. Peel, wash and cut the potatoes into pieces.
Clean and wash the spring onions. Cut the green of one spring onion into fine rings, remaining spring onions diagonally into pieces of approx. 2 cm length. Knead minced meat with leek onion green, egg yolk, salt, pepper and mustard.
Form small dumplings with moistened hands. Wash the dill, dab dry and cut finely. Heat the oil in a pan. Brown the meatballs all around and take them out. Brown the cucumber and potatoes in the frying fat.
Deglaze with broth and stew covered for about 15 minutes. Add spring onions and dumplings and cook for another 5 minutes. Mix sour cream and cornstarch. Add to the ragout and bring to the boil briefly. Add dill.
Season to taste with salt and pepper. Serve in a preheated bowl.