Preheat a steam oven to 350 degrees F.
Remove the cabbage and then rinse under hot water until all the spices are dissolved and the cabbage is clean. Steam in a baking tray in the oven until softened, 1 hour. Keep warm until ready to serve.
For the haddock: Bring the milk, 1 cup water, the thyme and bay leaf to a simmer. Add the haddock and poach until cooked, 3 minutes.
For the beurre blanc: Heat the white wine, vinegar, shallots, bay leaf and thyme. Reduce the liquid by half. Add the cream, and reduce by half again. Whisk the butter into the cream reduction. Remove from the heat, then reserve.
Assemble the warmed sauerkraut on the center of each plate in a circular mound. Arrange the fish across the top of the sauerkraut: first the haddock, then the salmon and finally the halibut. The two mussels are place on opposite sides of each other, beside the fish. Drizzle the beurre blanc sauce around and over the fish. Garnish each plate with the diced tomato, chopped chives and dill.