Pulse the pistachios along with 25 grams of granulated sugar, in a food processor, until finely ground. Set aside
In the bowl of a stand mixer add 125 grams of granulated sugar and the orange zest and massage together with finger tips, or mix on low using the paddle attachment for about a minute.
Next add the butter and pistachio/sugar mixture and beat on medium speed for 2-3 minutes or until well combined.
Add the egg yolk and beat until well combined.
In a separate bowl whisk together the flour, almond flour, baking power and salt.
Add the dry ingredients to the mixer bowl and beat on low until everything is just combined.
The dough will be a bit crumbly so use your hands to bring it together.
Roll the dough into a rough rectangle ½” thick. Wrap in plastic and chill for about 30 minutes in the fridge. (At this point the dough can be frozen and cut at a later time)
Remove the dough from the refrigerator and cut strips 1”wide, then cut 1” wide strips at a 45º angle from the first cuts. You should end up with a diamond shape.
Place the cookies on a parchment lined baking sheet. Brush the tops with the egg white and sprinkle with powdered sugar.
Bake at 350ºF for 113-14 minutes, or until a light golden brown.
Remove from the oven and let the cookies cool for 5 minutes, then place them on a wire rack to cool completely.