Place fish fillets skin-side down on a parchment-lined sheet pan or ovenproof baking dish and sprinkle with a generous layer of salt and pepper.
Combine crème fraîche, Dijon mustard, whole-grain mustard, minced shallots, drained capers, salt, and pepper in a small bowl.
Spoon the mustard sauce evenly over the fish fillets, making sure each of the fillets is completely covered.
Bake at 425°F for 10 to 15 minutes, depending on the thickness of the fillet.
Serve hot or at room temperature, making sure to spoon more of the sauce over the top of the fillets.
