Finely grind the almonds with the flour, ginger and baking powder in a food processor.
Beat the butter, brown sugar and white sugar until light. Add the zest, egg yolk and vanilla and beat well. Mix in the dry ingredients and beat until just blended. Stir in the pistachios.
Divide the dough in half. Using floured hands, roll each half on a lightly floured surface into a 30cm log. Place logs on the prepared baking tray 10cm apart. Cover with plastic wrap and refrigerate for about 1 hour.
Preheat oven to 180 degrees C. Brush logs with beaten egg and sprinkle with 2 teaspoons white sugar. Bake logs until deep golden brown and firm to the touch, about 30 minutes. Let logs cool for 10 minutes.
Reduce oven temperature to 150 degrees C.
Using a serrated knife cut logs crosswise into 1cm thick slices. Arrange slices on baking tray. Bake until deep golden on top, about 12 minutes. Turn biscotti over and bake other side until deep golden, another 12 minutes. Transfer biscotti to a rack and cool completely. Store in an airtight container at room temperature.