Clean and peel the cucumbers, cut them in half lengthwise. Scratch out the seeds with a spoon. Coarsely chop the cucumbers. Clean, wash and cut spring onions into rings.
Heat butter in a large pot. Sauté cucumbers and spring onions in it until translucent. Pour wine and 1⁄2 l water, stir in broth. Bring everything to the boil, cover and simmer for about 15 minutes until the gherkins are soft.
In the meantime cut salmon into strips. Wash the dill and shake dry. Pluck the dill flags from the stalks and cut finely.
Finely puree the soup with a hand blender. Stir in crème fraiche and dill. Season to taste with salt and pepper. Serve the soup and sprinkle with salmon and capers.