Combine the crème fraîche, two mustards, shallots, capers, 1 teaspoon salt, and 1/2 teaspoon pepper in a small bowl. Spoon the sauce evenly over the fish fillets, making sure the fish is completely covered. Bake for 10 to 15 minutes, depending on the thickness of the fish, until it’s barely done. (The fish will flake easily at the thickest part when it’s done.) Be sure not to over cook it! Serve hot or at room temperature with the sauce from the pan spooned over the top.