Heat oven to 350 degrees. Grease 13x9x2-inch baking pan.
Heat chocolate and shortening in a 3-quart saucepan over low heat until melted; remove from heat. Stir in sugar, eggs, and vanilla. Mix in remaining ingredients. Spread in pan.
Bake until brownies begin to pull away from sides of pan, about 30 minutes. Do not overbake.
Cool slightly, spread with Glossy Chocolate Frosting (below), if desired. Cool completely; cut into 2x1.5-inch bars. Makes 3 dozen cookies.