Preheat oven to 375 degrees F. Bake pastry shell 10 minutes; remove from oven. Reduce oven temperature to 325 degrees. In saucepan, over low heat, melt chips with margarine. In mixer bowl, beat chocolate mixture with Eagle Brand®, biscuit mix, eggs and vanilla until smooth. Add nuts. Pour into pastry shell. Bake 35 to 40 minute or until center is set. Serve warm or at room temperature with ice cream. Refrigerator leftovers.