For the meatballs peel onions. Halve 1 onion and finely dice the rest. Knead minced meat, breadcrumbs, mustard, half onion cubes and 4 tbsp. milk. Season with salt and pepper. Form approx. 20 balls from the minced meat mixture.
Boil up approx. 1 l salted water, onion halves, bay leaf and juniper. Let the meatballs simmer for about 10 minutes.
Meanwhile peel the cucumbers, cut them in half lengthwise and remove the seeds. Depending on the size, halve the cucumber halves again lengthwise, then cut into slices. Remove meatballs from the stock with a skimmer. Sieve the stock and measure approx. 500 ml.
For the vegetables heat butter in a pot. Fry the remaining onion cubes until translucent. Add cucumbers and fry briefly. Add 500 ml stock, bring to the boil, cover and simmer for about 5 minutes.
Stir flour and approx. 6 tbsp. water until smooth. Stir into the vegetables, bring to the boil and simmer for about 5 minutes. Season vegetables with salt and pepper. Add meatballs and capers to the vegetables and heat up. Parsley potatoes go well with them.