Preheat and Prepare the Potatoes: First, preheat your oven to 200°C (180°C Fan/Gas Mark 6). On a large, rimmed baking sheet, toss the potato chunks with the olive oil, 1 teaspoon of sea salt, and ½ teaspoon of black pepper. Spread them out into a single, even layer, making sure they aren't crowded. This space is key for roasting, not steaming.

First Roast for the Potatoes: Place the baking sheet in the preheated oven and roast for 20 minutes. We're looking for them to start softening and developing golden, lightly browned edges.

Make the Lemon Butter Sauce: While the potatoes are having their first roast, prepare the star of the show. In a small bowl, whisk together the melted butter, minced garlic, the juice of half a lemon, half of the chopped dill, and half of the chopped parsley.

Assemble the Sheet Pan: Carefully remove the baking sheet from the oven. Push the partially cooked potatoes to one side of the pan. Pat your salmon fillets dry with a paper towel – this is an important step to help the sauce stick and to ensure the fish roasts nicely.

Add the Salmon and Sauce: Arrange the salmon fillets on the empty side of the baking sheet. If you're using asparagus, add it to the pan now, tossing it lightly with the potatoes. Spoon the glorious lemon butter sauce evenly over each salmon fillet.

Final Seasoning and Garnish: Season the salmon fillets with a little more salt and pepper. Lay a couple of the thin lemon slices on top of each fillet. This not only looks beautiful but also infuses the fish with more citrus aroma as it cooks.

Roast Everything Together: Return the full sheet pan to the oven. Roast for another 12-15 minutes. The exact time will depend on the thickness of your salmon. The dish is ready when the potatoes are golden brown and wonderfully crispy, and the salmon is opaque and flakes easily when gently pressed with a fork. According to the Food Standards Agency, fish should be cooked until it's steaming hot and cooked all the way through.

Rest and Serve: Remove the pan from the oven. Sprinkle everything with the remaining fresh dill and parsley for a burst of fresh flavour. Serve your delicious Lemon Butter Salmon Crispy Potatoes immediately, straight from the pan.