Let the salmon fillets defrost for 1 hour if necessary. Cut the pointed cabbage into strips, dice the onion.
Melt the butter in a saucepan and sauté the onion cubes. Add the pointed cabbage strips and sauté while stirring. Deglaze with vegetable stock and season with salt and pepper. Steam everything for 10 minutes. Drain the pointed cabbage in a sieve while collecting the cooking liquid. Make up to 250 ml with water and pour back into the pot.
Peel the potatoes, cut into slices, mix with the cabbage strips and place in a flat baking dish. Season the dried salmon with salt and pepper and place on top of the cabbage and potato mixture. Add the cream to the cooking liquid, season with mustard and dill and season with salt and pepper. If necessary thicken with a little wheat flour. Pour the sauce over the salmon.
Bake in the oven at around 180 ° C for around 25 minutes.