Heat oven to 350°F. In 2-quart saucepan, melt butter over medium heat. Cook onion in butter, stirring occasionally, until tender. Stir in flour; cook until mixture is smooth and bubbly. Gradually add half-and-half, salt and pepper. Heat to boiling, stirring constantly, until thick. Remove from heat; stir in turkey, asparagus, mushrooms and wine.