1 1/2 pound bittersweet chocolate, chopped
6 tablespoons unsalted butter, cut into pieces
1 1/2 cup roughly chopped, toasted pistachios
1 1/2 cup cold heavy cream
1. Line a lightly oiled 6-cup loaf pan with plastic wrap and set aside.
2. In the top of a double boiler or in a metal bowl set over a pan of simmering water, combine the chocolate and butter and melt until smooth, stirring occasionally. Remove from the heat and fold in the pistachios. Let cool.
3. In a bowl fitted with an electric mixer, beat the heavy cream until stiff peaks form. Whisk about one-third of the cream into the cooled chocolate, then gently fold in the remaining whipped cream. Pour the chocolate mixture into the prepared pan, smoothing the top with a rubber spatula. Cover with plastic wrap and chill it overnight.
4. Unwrap the pan, invert onto a serving platter, and shake gently to release. Remove the plastic wrap from the top and let sit at room temperature about 15 minutes to soften. Slice into 1/2-inch to 3/4-inch slices and serve with the Orange Creme Anglaise.