- Preheat oven to 175 degrees Celsius.
- Cut the fish into strips and lightly salt.
- Roll the fish fillets, greased inside with butter.
- In a small skillet, sauté the onions and celery in butter until golden brown.
- Add 1 teaspoon salt, ground pepper, sage, and bread cubes to the vegetable/oil mixture. Add some hot water if the filling feels too dry.
- Fill the fish rolls with this mixture (spoon at a time). Sprinkle with chopped parsley.
- Bake in the preheated oven for 30 minutes. Check readiness with a fork.