These chocolate biscotti are made with chopped pistachios but would also be great with almonds or any nut, really. They are twice-baked: the cookie dough is baked as a log, then sliced into cookies, which are baked again to dry them out and crisp them up. These biscotti store well.
Preheat the oven to 350 °F (175 °C). Line a baking sheet with parchment (stick to a lighter coloured cookie sheet to avoid overbaking/burning the biscotti).
In a food processor, combine the flour, baking powder, and salt. Then drop in the butter chunks and pulse to form a coarse meal texture. Add the egg, milk, and vanilla, and pulse again a few times.
Transfer the dough to a bowl to work in the pistachios by hand (if you do this in the food processor, you risk grinding the nuts too much).
Pat the dough into a flattened roll with well floured hands (dough is sticky!) and form it into a loaf about 12 inches long on the parchment-lined sheet.
Bake for 30 minutes.
Let the roll cool for 10 minutes, then using an electric carving knife, cut the roll into ¾-inch thick biscotti.
Transfer the cookies to the baking sheet, and bake them again for 20–25 minutes. Watch them because you don't want them to burn.