Preheat oven to 325°F/163°C and grease a 13"x9" pan. In a small saucepan, melt butter and cocoa then let to cool slightly. In a large bowl, beat together sugar and eggs until smooth then add the cocoa/butter mixture for 1 minute. Add salt, flour, milk, and vanilla, mix beat together for 1 more minute. Fold in nuts. Spread onto 13"x9" pan and bake for 30 minutes.