Coat a 13x9x2-inch baking pan with nonstick cooking spray. Set pan aside.
In a large bowl, combine sugar and cocoa powder. Add butter, honey, and vanilla; beat with electric mixer on low speed until combined. Add eggs, one at a time, beating well after each addition.
Gradually add flour and salt, beating on low to medium speed until just combined. Stir in walnut pieces. Spoon into prepared baking pan.
Bake in a 350 degree F oven about 35 minutes or until a toothpick inserted near the center comes out clean. Remove brownies from the oven; cool completely on wire rack before frosting.
Spread Chocolate Frosting evenly over brownies. Allow frosting to set before cutting into squares. Makes 24 to 32 brownies.
In a medium bowl, combine powdered sugar, unsweetened chocolate, and butter. Beat with an electric mixer on low speed until combined. Slowly add boiling water, beating until evenly blended and smooth.