Preparation

• Position a rack in the center of the oven, and heat the oven to 325°F. Lightly grease (or line with parchment) a large rimmed baking sheet.
• In a stand mixer fitted with the paddle attachment (or with a hand-held mixer and a large bowl), beat the butter, sugar, salt, vanilla, and baking powder until smooth, about 1 minute. Beat in the eggs, and then beat in the flour at low speed until blended; the dough will be sticky. Stir in the pistachios and cherries.
• Divide the dough in half, and transfer both halves to the prepared baking sheet, leaving space between them. Shape each half into a rectangle about 10-1/2 inches long by 2 inches wide by 3/4 inch tall. Straighten the edges, and smooth the tops; a wet spatula works well here.
• Bake for 30 minutes, then remove from the oven. Using a spray bottle filled with room-temperature water, lightly but thoroughly spritz the two pieces of dough all over. This will make slicing the biscotti easier. Carefully transfer the dough to a cutting board. Using a sharp chef’s or serrated knife, cut the biscotti on the diagonal, about 1/2 inch to 3/4 inch wide. As you’re slicing, be sure to cut straight up and down, perpendicular to the cutting board.
• Place the biscotti on the same baking sheet, on edge; they can be very close together. Return the biscotti to the oven, and bake for 25 to 27 minutes, until they feel very dry and are beginning to turn golden. Smaller biscotti may be ready to come out of the oven earlier than the larger ones. Let cool on the baking sheet for 2 minutes, then transfer to a wire rack to cool completely.
• Dip one end of each cooled biscotti in the melted chocolate, then place on a parchment-lined baking sheet to set. Sprinkle with the chopped pistachios while the chocolate is still soft, if you like. Once the chocolate has set, store the biscotti in an airtight container at room temperature for 1 week; for longer storage, wrap airtight and freeze.