For the brownie batter:. Melt the butter and chocolate squares in a double boiler, stirring every 30 seconds, until completely melted. Let cool slightly before stirring in the sugar. Beat in the eggs and vanilla until well combined. Sift in the flour and cinnamon and mix. Fold in 1 cup chopped walnuts and 1/2 chopped pistachios. Set brownie batter aside.