Coat the cookie sheet with nonstick cooking spray. Set aside. In a small mixing bowl, stir together the flour, cocoa powder, baking soda, and salt.
In a medium mixing bowl, beat butter with an electric mixer for 30 seconds. Add the brown sugar. Beat until well combined. Add buttermilk, egg product or egg whites, and vanilla. Beat until combined.
Add the flour mixture to the beaten mixture and mix well. Drop the dough by tablespoonfuls onto a prepared cookie sheet. Bake cookies in a 350 degree F oven for 7 to 9 minutes or until nearly firm. Cool on cookie sheet for 1 minute. Remove to wire rack. Cool completely. Sprinkle the cookies with powdered sugar. Makes 24 cookies.