In a large bowl, combine first five ingredients. With a pastry blender, cut in shortening until evenly distributed. Store in a large airtight container in cupboard. Keeps 10-12 weeks. Yield: about 17 cups of mix.
To prepare brownies: In a bowl, combine the first four ingredients. Beat with spoon until smooth. Spread into a greased 8-in. square baking pan. Bake at 350° for 20-25 minutes or until top tests done. Cut into squares while still warm. Dust with confectioners' sugar if desired.