4 tbsp. butter, melted
1 1/2 lbs. rock cod fillets, skin and bones removed
Salt
Pepper
2 tbsp. olive oil
3 c. leeks (white part only), peeled & thinly sliced
1/3 tsp. ground thyme
1/4 c. parsley, chopped
2 lbs. boiling potatoes, peeled & sliced into 1/8-inch rounds

Brush 9 x 12-inch baking dish with about 1 tablespoon melted butter. Lay rock cod fillets in a single layer on the bottom of the dish. Sprinkle with salt and pepper.

Heat 1 tablespoon olive oil in 12-inch skillet. Add leeks and thyme, and salt and pepper lightly. Cover and cook over medium heat 5 to 6 minutes, until leeks are soft, but not brown. Stir frequently.

Spread leek mixture over fish and sprinkle with parsley. In the same pan, over medium heat, add 1 tablespoon melted butter and remaining olive oil. Add potatoes, spreading them evenly over bottom of pan. Cook about 10 minutes, stirring pan frequently. Spread partially cooked potatoes over fish. Pour remaining melted butter over gratin and bake in 450 degree oven 25 to 30 minutes, basting with juices 2 or 3 times. Serve when potatoes are well browned. Serves 4 to 6.