Preheat oven to 200ºC . Wash and pat dry salmon steaks.
In a large, deep, ovenproof skillet or stovetop casserole over medium high heat, saute salmon briefly on each side in butter and oil (about 1 minute). Remove to a platter.
Add saffron, garlic, tarragon, thyme, sage, bay leaves, tomatoes, olives, wine, fish stock, and salt substitute. Bring to a boil. Lower heat and simmer for 10 minutes, uncovered.
Add salmon steaks. Remove pan from heat and place in oven. Bake until salmon is lightly pink and done to taste (10 minutes).
To serve, place salmon steaks on platter and spoon sauce over them.