Heat butter and brown sugar with nuts in saucepan until melted. Spread in bottom of pie shell. Bake at 450° for 5 minutes in oven. Cool. Prepare pie filling mix with milk as directed for pie; cool 5 minutes, stirring occasionally. Measure 1 cup; cover with wax paper and chill thoroughly. Pour remainder into pie shell; chill. Prepare whipped topping mix as directed. Fold 1 1/3 cups into the 1 cup of chilled pie filling. Spread over filling in pie shell. Chill. Garnish with remaining whipped topping and additional pecans, if desired.