Position rack in middle of oven. Preheat oven to 450°F (230°C). Use 1 tablespoon of butter to coat the insides of a 13 by 9 inch (33 cm by 23 ccasserole dish or similar sized roasting pan; set aside.

Combine the remaining melted butter with the garlic-infused olive oil. Layer the potatoes in your buttered dish, slightly overlapping to create one layer covering the entire bottom of the pan. Brush potatoes with butter/oil mixture and season with salt and pepper. Make another layer of potatoes, brushing with butter/oil and seasoning as you go until you use up all of the potatoes. Brush tops of potatoes with butter/oil, reserving some for the fish. Season with salt and pepper and cover pan tightly with foil. Roast for 15 minutes, then remove foil and continue roasting until potatoes are golden brown and beginning to crisp up, about 15 to 20 more minutes.

Meanwhile, season fish with salt and pepper. Zest the lemon and toss lemon zest with parsley; set aside.

Once the potatoes have finished their initial cooking time, lay the bluefish on top. Brush with remaining butter/oil mixture and roast for about 10 to 12 minutes or just until fish is opaque and cooked through. It should flake easily. Right before serving sprinkle the fish and potatoes with lemon juice and shower with parsley/zest mixture. Serve immediately.