In a small saucepan, melt the butter. Stir in the brown sugar and bring to boiling. Stir in the whipping cream and return to boiling. Add the nuts. Pour into the baked pastry shell and set aside.
In a medium saucepan, stir together the 2 cups half-and-half and the 2/3 cup sugar. Heat to simmering, stirring occasionally. Don't boil.
In a small bowl, stir together cornstarch, flour, the 1/2 cup half-and-half, and egg yolks. Stir into filling mixture. Cook and stir over medium heat until thickened and bubbly; cook and stir 2 minutes more. Remove from heat; stir in vanilla. Cover saucepan to keep filling hot while making meringue.
In a large mixing bowl, combine egg whites, vanilla, and cream of tartar. Beat with an electric mixer on medium speed for 1 minute or until soft peaks form (tips curl). Gradually add the 6 tablespoons sugar, 1 tablespoon at a time, beating on high speed for about 4 minutes more or until mixture forms stiff, glossy peaks (tips stand straight) and sugar dissolves.
Pour hot filling over caramel layer. Immediately spread meringue over hot pie filling, making sure meringue seals to edges of pastry to prevent shrinkage.
Bake the pie in a 350 degree F oven for 15 minutes. Cool on a wire rack for 1 hour. Chill the pie for 3 to 6 hours before serving. Cover for longer storage. Makes 10 servings.
Stir together flour and salt. Using a pastry blender, cut in shortening until pieces are pea-size. Sprinkle 1 tablespoon cold water over part of the mixture; gently toss with a fork. Push moistened dough to the side of the bowl. Repeat moistening dough, using 1 tablespoon cold water at a time, until all the dough is moistened (4 to 5 tablespoons cold water total). Form dough into a ball. On a lightly floured surface, use your hands to slightly flatten dough. Roll dough from center to edge into a circle about 12 inches in diameter. To transfer pastry, wrap it around the rolling pin. Unroll pastry into a 9-inch pie plate. Ease pastry into pie plate, being careful not to stretch pastry. Trim pastry to 1/2 inch beyond edge of pie plate. Fold under extra pastry. Crimp edge as desired. Generously prick bottom and side of pastry in pie plate with a fork. Prick all around where bottom and side meet. Line pastry with a double thickness of foil. Bake in a 450 degree F oven for 8 minutes. Remove foil. Bake 5 to 6 minutes more or until golden. Cool on a wire rack.