Heat oven to 375°F. Grease bottom and sides of 15x10x1-inch pan with shortening or cooking spray. In large bowl, mix flour, granulated sugar, 4 teaspoons cocoa and espresso.
In 1-quart saucepan, heat water and 3/4 cup butter to boiling. Pour over flour mixture; beat with spoon until smooth. Stir in baking soda, 1/3 cup buttermilk and the egg. In pan, spread batter evenly.
Bake 18 to 23 minutes or until toothpick inserted in center comes out clean. Cool completely, about 1 hour.
In 3-quart saucepan, heat 1/4 cup cocoa, 1/2 cup butter and 1/3 cup buttermilk to boiling over medium heat, stirring frequently; remove from heat. Stir in powdered sugar, 1 teaspoon espresso and vanilla with wire whisk until smooth and spreadable. Spread frosting over brownies. For brownies, cut into 10 rows by 5 rows.