Preheat the oven to 350F. Bring a pan of water to a boil and blanch the onions for 3 minutes. Drain. Melt half the butter in a frying pan and cook the onions, covered over low heat, for 10 minutes. Spoon the onions into a roasting pan and place the trout on top. Dot with remaining butter. Pour in the wine. Season with salt and pepper. Bake for 10 mintues.
