Butter and flour large baking sheet. Finely grind almonds with flour, ginger, and baking powder in processor. Beat butter, brown sugar and 1/4 cup sugar in large bowl until well blended. Add orange peel, egg and vanilla and beat well. Add dry ingredients and beat just until blended. Stir in pistachios.
Divide dough in half. Using floured hands, roll each half on lightly floured surface into 12" x 2" log. Arrange logs on prepared sheet, spacing 4 inches apart. Cover with plastic wrap and refrigerate until cold, about 1 hour.
Preheat oven to 350 degrees F. Brush dough logs with some of egg glaze. Sprinkle with two teaspoons of sugar. Bake until deep golden brown and firm to touch, about 30 minutes. Transfer baking sheet to rack and cool logs 10 minutes. Reduce oven temperature to 300 degrees F.
Using serrated knife, cut logs crosswise into 1/2 inch thick slices. Arrange slices cut side down on baking sheet. Bake until deep golden on top, about 12 minutes. Turn biscotti over and bake until deep golden, about 12 minutes. Transfer biscotti to rack and cool completely.
Can be made 3 days ahead. Store at room temperature in an air-tight container.