Heat oven to 350 degrees F. Spray a 9 x 13-inch pan lightly with cooking spray.
Line bottom with parchment paper.
In a mixing bowl with electric mixer, blend melted butter with granulated and
brown sugar, then add vanilla extract and eggs. Blend well on slow speed.
In a separate bowl, stir together cocoa, flour, baking soda and salt. Fold into
batter and blend well, scraping bottom of mixing bowl to ensure ingredients are
evenly combined. Fold in nuts if using.
Pour or spoon into prepared pan. Place pan on a cookie sheet (this protects bottoms
from over baking while top bakes.) Bake until done (35-40 minutes). Brownies will
be set and slightly firm, but not dry.
Cool, then freeze 1 hour before cutting.
Unmold before cutting. Peel off parchment paper. Cut into large 2 1/2 x 3-inch
blocks. Wrap each in wax paper and keep refrigerated or frozen.
To serve for a party, pile brownies on platter and dust with confectioners sugar.