Meanwhile, in top of double boiler, mix sugar, flour and 1 teaspoon salt. In medium bowl, beat milk and egg yolks together with whisk or fork; beat into dry ingredients in top of double boiler. Cook over hot water 10 to 12 minutes, stirring constantly, until thickened. Stir in 1/2 teaspoon vanilla. Pour onto chocolate layer; refrigerate 4 hours. Just before serving, arrange pound cake pieces over pie. Drizzle reserved chocolate mixture over pie. Top with crust cutouts. Cover and refrigerate any remaining pie.