Coarsely chop 1 1/2 cup nuts. In medium saucepan, over low heat, stir condensed milk, margarine and cocoa until margarine melts and mix is warm; remove from heat. Stir in eggs, flour, vanilla, and chopped nuts; pour into prepared pie crust. Bake at 350~F for 50 minutes or until center is firm. Serve warm or cold garnished with whipped cream and remaining nuts.