For the cucumber-salmon salad with cress, remove the center bone from the salmon. For the fish stock, rinse, clean and coarsely chop the greens.
Boil with two liters of water, salt, salmon bones, bay leaf, juniper berries, mustard seeds and the quartered lemon for 20 minutes with the lid closed.
Chop the belly flaps from the salmon pieces. Add the salmon to the slightly boiling stock and put the lid on the pot. Remove from the heat and do not let it cool completely.
In the meantime, line a colander with a dishcloth. Peel the cucumber, cut in half lengthwise and scrape out the seeds. Finely dice the cucumber, sprinkle lightly with salt and let drain in the prepared colander.
For the mayonnaise, mix salt, egg yolks, juice of one lemon and mustard in a mixing bowl. Add the oil to the eggs drop by drop at the beginning, then in a thin stream with the whisks from the mixer.
Mix the finished mayonnaise with six tablespoons of strained fish stock. Remove the fish from the stock, removing the skin and gray parts.
Cut the fish into bite-sized pieces, thoroughly removing any remaining bones. Season the fish with pepper and squeeze the cucumber cubes in the dish.
Trim the cress with kitchen shears. Alternate layers of salmon, cucumber and mayonnaise in a suitable bowl, sprinkling each layer of mayonnaise with cress.
Dress the finished cucumber-salmon salad with cress with a little more cress.