In the bowl of an electric mixer, cream butter for about 2 minutes on medium speed. Add sifted powdered sugar to the butter one tablespoon at a time. Cream mixture for 2-3 minutes, until fluffy and lightened in color.
Add vanilla and mix until incorporated.
Add ground pistachios and mix on medium speed until incorporated. Don’t forget to scrape your bowl at every step to make sure everything is getting incorporated.
Add orange juice and orange zest to the bowl and mix. Add all-purpose flour and salt and stir with a spatula or on the lowest speed of your mixer for about 30 seconds just until the flour is incorporated.
Your dough will be very wet and that’s ok. I pat it into a disk and lightly sprinkle powdered sugar on both sides and wrap it in plastic wrap.
Refrigerate for 2-4 hours or overnight. This is a very important step. Leave dough in the fridge until it’s been entirely chilled. Check by poking the middle of the dough. If it’s soft, means the dough has to rest longer.
Remove dough from the fridge and divide into 2 parts. Keep the part you are not working with in the fridge, covered with the plastic wrap.
Roll the other half on a floured counter until it’s 1/4” thick. Dough might be very hard at first. Give it a couple of minutes to soften up slightly.
Cut into rounds, stars, or rectangles, whatever shape you want to work with. Place on a baking sheet lined with parchment paper or with a silicon mat.
Place tray in the freezer while you pre-heat your oven.
This step is also important because when you roll out the dough, the butter softens up. You want the butter to be very cold and solid before entering the oven. This helps your cookie retain a better shape and structure because the butter won’t start melting immediately.
Pre-heat the oven to 350F.
Bake trays anywhere from 10-20 minutes. It depends on the size of the cookies you are making. Speaking about size, if your cookies are very large, say, over 1 1/2 inches long or wide, you want to lightly poke the top of the cookies with a fork before inserting in the oven. If you don’t do that, air bubbles will form and change the shape of the cookies.
Remove cookies from the oven once center is lightly blonde and outsides are lightly golden. That's the perfect balance for looks and texture! Don’t overbake your Shortbread cookies or they will be tough.
Once cookies are cooled, melt chocolate over a double boiler. Dunk one end of each cookie in melted chocolate and scrape excess with a small spatula. Sprinkle powdered pistachio over chocolate and let it dry on a wire rack.