Preheat your oven to 450°F (232°C). Grease an 8×8 baking dish and combine the Yukon gold potatoes with extra-virgin olive oil, kosher salt, and freshly cracked black pepper. Toss until evenly coated. Spread the potatoes in a single layer and roast for 20-25 minutes, or until they are tender and golden brown, turning them halfway through for even cooking.

While the potatoes roast, melt 2 tablespoons of salted butter and heat 2 tablespoons of the remaining olive oil in a saucepan over medium heat. Sauté the shallot for about 5 minutes until soft and translucent, then add minced garlic and cook for an additional minute until fragrant. Pour in 1 cup of heavy cream and ½ cup of chicken or fish stock, then stir in fresh rosemary, lemon zest, lemon juice, Dijon mustard, cayenne pepper, and capers. Simmer the sauce for 5-7 minutes until thickened.

Once the potatoes are roasted, remove them from the oven and lower the temperature to 400°F (204°C). Season the cod fillet with kosher salt, and place it amongst the golden roasted potatoes in the baking dish. Pour the warm rosemary cream sauce over the cod and potatoes, ensuring everything is well coated for maximum flavor.

Bake the assembled dish uncovered in the oven for 10-15 minutes. The cod is done when it flakes easily with a fork and has turned opaque. Remove the baking dish from the oven and let it sit for a couple of minutes before garnishing with chopped fresh parsley. Serve your Cod & Potatoes in Rosemary Cream Sauce hot, paired with crusty bread or a crisp green salad for a complete meal.