01 - Preheat the oven to 400°F. Lightly grease a baking dish large enough to hold the cod fillets in a single layer.
02 - Pat cod fillets dry with paper towels. Season both sides evenly with salt and black pepper. Arrange fillets in the prepared baking dish in a single layer.
03 - In a small saucepan over medium heat, melt the butter with olive oil. Stir in lemon juice, lemon zest, and capers. Cook for 1 to 2 minutes until fragrant, then remove from heat.
04 - Spoon the lemon butter sauce evenly over the cod fillets, ensuring even coverage.
05 - Bake for 15 to 18 minutes, or until the cod is opaque and flakes easily when tested with a fork.
06 - Remove from the oven. Sprinkle with fresh parsley and garnish with lemon slices if desired. Serve immediately.