Prepare Potatoes: Boil or roast evenly sliced potatoes until tender; season with salt and pepper.
Prepare Cod: Pat fillets dry; season with salt and pepper. Sear in skillet with olive oil or butter 3–4 minutes per side until golden and flaky. Optional: bake at 375°F (190°C) for 8–10 minutes.
Make Rosemary Cream Sauce: Sauté garlic and onion in butter until translucent. Add cream and rosemary; simmer gently, reducing slightly. Optional: add white wine, lemon juice, or Parmesan for added flavor.
Assemble Dish: Layer potatoes on plates or in pan, top with cod fillets, and pour cream sauce over. Optional: briefly broil for golden tops and slight caramelization.
Garnish & Serve: Add fresh rosemary, lemon wedges, or microgreens before serving.
