In a bowl, combine cocoa, flour, and salt. Stir and set aside.
In a small saucepan, melt butter and shortening over low heat. When melted, remove from heat and allow to cool slightly.
In mixing bowl, beat together eggs, sugar, and vanilla. Mix in butter mixture. Add dry mixture about a half at a time, mixing well. Be sure to scrape bowl. Stir in nuts.
Spread evenly into baking dish. Bake 25 - 30 minutes, until a toothpick inserted in center comes out clean. Cool completely.