Grease a large-sized baking dish with 1 tbsp (0. 5 oz / 15ml) of olive oil and preheat your oven to 400°F (200°C).
Place the 16 oz (454g) salmon fillet on the baking dish, preferably skin-side down, and generously season with 0. 5 tsp (2. 5g / 0.18 oz) of sea salt and 0. 25 tsp (0. 5g / 0.18 oz) of ground black pepper.
Thinly slice half of the lemon and place the slices evenly over the salmon.
Cover the fish with 3 tbsp (1. 5 oz / 42. 5g) of the butter, cut into very thin slices.
Bake on the middle rack for 25 to 30 minutes, or until the Keto Baked Salmon flakes easily with a fork and is entirely opaque.
While the fish rests, heat the remaining 3 tbsp (1. 5 oz / 42. 5g) of butter in a small saucepan over moderate heat until it begins to bubble, then immediately remove from the heat and let it cool slightly.
Gently squeeze the remaining half of the lemon to yield about 1 tbsp (0. 5 oz / 15ml) of fresh lemon juice, and whisk it into the slightly cooled melted butter.
Pat it Dry: Always pat your salmon fillets completely dry with a paper towel before seasoning. Removing excess surface moisture ensures the butter and seasonings adhere properly and prevents the fish from steaming instead of baking.