Clean the livers by removing any connective tissue and cut them in half. Pat dry on paper towels. Heat the butter and oil, add the mushrooms and onions and saute until nicely brown, stirring occasionally. Add the chicken livers and cook for 5 to 6 minutes. Season with salt and pepper. Add the wine and cook, stirring to incorporate any pan drippings for an additional minute or two. Adjust the seasonings. Serve on squares of hot buttered toast and garnish with parsley.