Peel and dice the onions. Peel and dice the kohlrabi. Sauté the onions in oil. Add the kohlrabi and sauté briefly. Pour in the broth and simmer for about 10 minutes until it has the right bite. Add the cream, mustard, sugar, lime juice and chives and season with salt and pepper.
Meanwhile, season the salmon fillet with salt and pepper and fry in oil. First put the kohlrabi sauce on plates and place the salmon fillet on top.