6 tablespoons unsalted butter, at room temperature
2 1/4 cups sugar
5 large eggs, at room temperature
1/2 cup salted pistachios, chopped
1/2 cup chopped dried cherries
Preheat the oven to 350°. Toast the hazelnuts in a pie plate for 12 minutes, until the skins blister. Transfer to a towel and rub to remove the skins. Coarsely chop the nuts.
In a large bowl set over a pan of simmering water, melt 1 pound of the bittersweet chocolate with all of the unsweetened chocolate. Let cool completely.
In a small bowl, whisk the flour, baking powder and salt. In the bowl of a standing electric mixer fitted with the paddle, beat the butter at medium speed until creamy. Beat in the sugar until sandy. Beat in the eggs, then beat in the melted chocolate. At low speed, beat in the dry ingredients. Fold in the pistachios, cherries, hazelnuts and the remaining bittersweet chocolate.
For each cookie, scoop 2 tablespoons of dough onto a parchment-lined baking sheet and roll into a ball; space them about 1 1/2 inches apart. Bake in batches for 15 minutes, just until the tops are lightly cracked; shift the sheets from top to bottom and front to back halfway through for even baking. Transfer the sheets to racks to cool slightly, then transfer the cookies to a rack. Serve warm or at room temperature.