Season fillets with salt and pepper and then dust with four. Heat 2 tablespoons of the butter and all of the oil in a large skillet over medium heat. Sauté fish on each side for 3 to 4 minutes or until just firm. Remove fillets and place on a warmed plate or platter. Add remaining butter and onions to skillet and sauté for 2 minutes. Increase heat to medium-high and add wine. Scrape the bottom of the pan to loosen any bits. Reduce liquid to 1 tablespoon. Add cream and cook until sauce thickens. Season with salt and pepper. Stir in shrimp and chives and return fish to skillet to warm.