If you must prepare your fish ahead, you can cook them in the poaching liquid very briefly, so they are still basically just raw in the center. Then you can set the pan in a low oven, about 180 degrees Fahrenheit, covered with parchment, and let the fillets finish cooking for 15 minutes or so.
People worry about what kind of wine to cook with.
While you don't need an extraordinary wine for the poaching liquid, you can't cook a good dish with a bad wine either. A useful principle is to make your poaching liquid with a wine that you would be happy to drink. All rights reserved.