In a large bowl, or in the bowl of your stand mixer, cream together the butter, confectioner's sugar (aka powdered sugar), and granulated sugar until light and fluffy, about 2-3 minutes. You want to see that the butter has lightened in color, and that some air has been incorporated into the mixture (= fluffiness).
Then, add in the almond extract, vanilla extract, and salt and mix again until completely incorporated.
Add in the flour and mix again until just combined. You don't want to have any streaks of flour, but you also do not want to over-mix the dough. The dough may be crumbly at this step.
Then, fold in the pistachios with a spatula until just combined.
Take out a long piece of plastic wrap and set it down on your counter. Place the dough on the plastic wrap in a log shape. Wrap the plastic wrap around the dough, and roll the log of dough onto the counter until it is cylindrical and 2" in diameter. Make sure all of the dough is compacted together.
Chill the dough in the refrigerator for AT LEAST one hour before baking, or up until overnight. The dough needs time to hydrate. The cookies will not work if they are not rested and chilled first, so don't skip this step!!
When it's time to bake, preheat your oven to 350 degrees F.
Using a sharp knife, cut the dough log into cookies about 1/2" thick. Space them out on a baking sheet lined with parchment paper, and bake in the oven for 12-13 minutes, or until just slightly browned on the edges (but not fully browned). You will need to use 2 separate baking sheets for this. Bake one sheet of cookies at a time, and keep the remaining dough chilled until ready to bake. If you only have one baking sheet, let that COMPLETELY cool before baking the next batch.
IMPORTANT: leave your cookies on the hot baking sheet after removing them from the oven, for at least 15 minutes. The cookies will continue to cook on the baking sheet.
After 15 minutes, you can move the cookies onto a wire rack to fully cool.
Enjoy!