Melt 4 chocolate baking squares and 1/2 cup butter in a heavy saucepan over low heat, stirring occasionally. Remove from heat, and transfer to a large bowl. Add sugars; stir well. Stir in eggs, 2 teaspoon espresso powder, and 2 teaspoon coffee liqueur. Add flour and salt, stirring until blended. Stir in pecans.
Spread batter into a lightly greased aluminum foil-lined 13" x 9" pan (or see note). Bake at 325° for 20 to 25 minutes or until brownies appear set on top. Cool completely in pan on a wire rack.
Melt remaining 2 chocolate baking squares and 2 Tbsp. butter in heavy saucepan, stirring occasionally. Remove from heat; transfer to a medium bowl. Stir in remaining 2 tsp. espresso powder, whipping cream, vodka, and remaining 2 Tbsp. coffee liqueur. Add enough powdered sugar to make a good spreading consistency, beating at medium speed with an electric mixer until smooth. Spread frosting over cooled brownies; garnish, if desired. Let stand until frosting is set. Use foil to lift uncut brownies out of the pan. Cut into bars to serve.
Note: For really thick, showy brownies, we baked these in an 11" x 7" pan at 325° for 26 to 28 minutes.
If you prefer not to add any alcohol to this dessert, you can use sweetened coffee Instead of the coffee liqueur and omit the vokda.