1. Heat oven to 350°F.
2. Melt butter in medium saucepan over low heat. Add cocoa; stir until smooth. Stir in sweetened condensed milk, water and eggs; beat with whisk until well blended. Remove from heat; stir in vanilla, maple flavor and walnuts. Pour into pastry shell.
3. Bake 40 to 45 minutes or until center is set. Cool slightly. Serve warm or cold. Garnish as desired. Refrigerate leftover pie. Makes 8 servings.