1. Preheat oven to 350 degrees F (175 degrees C).
2. In a small bowl, combine grated butter, olive oil, lemon juice, garlic, dill and salt.
3. Place fish fillets in a single layer in a medium baking dish. Pour the marinade on the fish.
4. Bake in the preheated oven for 30 minutes, or until the fish easily flakes with a fork.