Prepare Lattice-Crust Pastry; set aside.
Sauté mushrooms and onion in 1/4 cup butter in a large skillet 8 minutes or until vegetables are tender. Set aside.
Melt remaining butter in a small saucepan over low heat. Add flour, stirring until smooth. Cook 1 minute, stirring constantly. Gradually add broth and wine; cook over medium heat, stirring constantly, until thickened and bubbly. Stir in salt and pepper. Combine sauce, sautéed mushrooms, and onion; stir well.
Spoon mushroom mixture into pastry shell. Arrange pastry strips in lattice design over filling; seal edges and flute. Bake at 375° for 40 minutes or until browned.
Serving Suggestion: Mushroom Pie is an excellent side dish to serve with beef.
Oxmoor House Homestyle Recipes