Preheat oven to 350°F. Butter and flour 9 x 13-inch baking pan. Sift flour with salt into bowl. Using electric mixer, beat eggs in large bowl until frothy. Add sugar 1 tablespoon at a time and beat until pale yellow and slowly dissolving ribbon forms when beaters are lifted. Gently fold in melted chocolate. Add melted butter and vanilla and stir well (mixture may look curdled). Fold in flour. Fold in pistachios and chopped chocolate. Pour batter into prepared pan. Sprinkle additional chopped pistachios on top before baking. Bake until toothpick inserted in center comes out not quite clean, about 25 minutes; do not over bake. Cool in pan on rack. Cut brownies into squares.