Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper to prepare for baking.
In a large mixing bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking powder, and a pinch of salt.
In another bowl, cream the softened butter and superfine sugar together until light and fluffy. Add the eggs one at a time, mixing well after each addition.
Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to overmix.
Gently fold in the whole pistachios, distributing them evenly throughout the dough.
Transfer the dough onto a lightly floured surface and shape it into a log about 12 inches long and 3 inches wide. Place it on the prepared baking sheet.
Bake the log in the preheated oven for 25-30 minutes, or until it’s firm to the touch. Let it cool on the baking sheet for about 10 minutes.
Once cooled slightly, use a sharp knife to slice the log diagonally into 1-inch thick pieces.
Arrange the sliced biscotti cut-side down on the baking sheet and return them to the oven. Bake for an additional 10-15 minutes, or until they are crisp and dry.
Allow the biscotti to cool completely on a wire rack before serving.
