Put the onions on the bottom of a greased oven dish. Put the cod on top and sprinkle with salt and pepper. Pour the wine over the cod. Bake this in the oven at 180 degrees Celsius for 20 minutes. Pour the fluid in a pan and reduce on high heat to half. Turn off the heat and add the butter, whisking all the time, piece by piece. Finally, add the bread crumbs and pour this sauce over the fish. Put the lemon on top and sprinkle with parsley.