For the potatoes: Preheat oven to 400°F. Over low heat, melt 3 Tbsps. butter in a pan and set aside.
Peel Idaho potatoes and place in warm water to keep them from turning dark from oxidation. Remove one potato at a time and place with flat side against cutting board. Cut lengthwise into 1 /3-in. slices. Repeat with second potato.
Butter bottom of a sheet pan or Pyrex dish and place the potato slices in a single layer (use more than one pan if necessary). Brush the top of the slices with the melted butter and season to taste with salt and pepper. Place in oven for 20 minutes or until golden brown. Remove and keep in a warm place.
For the ling cod: Cut the ling cod into 8 pieces of equal size, removing any bones as you go. Season the flour with salt, pepper and herbs of your choice. Dust the pieces of cod with seasoned flour and bake for 15 minutes at 400°F. Remove from oven and keep warm.
To assemble the dish: Place 3 Tbsps. butter in sauté pan over high heat. Add sauerkraut and saute until partially golden brown; set aside.
Divide potato slices equally among entrée plates; top with sauerkraut and then cod.
Pour sauce over fish.
Serving suggestion: Garnish with scallions or chives and serve with organic vegetables.