1. Heat oven to 375°F. Bake pie crust 10 minutes; remove from oven to wire rack. Reduce oven temperature to 325°F.
2. Combine chocolate chips and butter in small saucepan. Cook over very low heat, stirring occasionally, until chips are melted. Combine chocolate mixture, sweetened condensed milk, baking mix, eggs and vanilla in large bowl; beat on medium speed of mixer until smooth. Stir in nuts. Pour into prepared pie crust.
3. Bake 35 to 45 minutes or until center is set. Cool. Serve warm or at room temperature with ice cream, if desired. Makes 8 servings.