For the cake: In a mixing bowl, combine flour, sugar, and salt. In a saucepan, melt butter then stir in cocoa and Pie Spice. Add boiling water and allow mixture to boil for 30 seconds. Remove from heat and pour cocoa mixture over flour mixture and stir lightly to cool. In a separate bowl, mix together buttermilk, beaten eggs, baking soda and vanilla. Stir buttermilk mixture into chocolate and flour mixture. Pour batter into a lightly buttered or oiled 18x13 sheet cake pan. Bake at 350 degrees for 20 min. For the icing: Melt butter in a saucepan then stir in cocoa and Pie Spice. Remove from heat, add milk, vanilla and powdered sugar and stir to combine. Fold in pecans and pour icing over warm cake. Let cake cool before serving.