First, mix the butter with the powdered sugar using a rubber spatula. You want to cream the both together until they are combined nicely.
Then, add 1 cup of flour at a time. Use the same spatula to mix it all together. When folding in the second cup, mix with your hands in order to have everything well incorporated. It should resemble pie dough. You want to be able to shape a disk or ball out of the dough. Don't be discouraged if the dough appears crumbly; keep working with it until it all comes together because it will!
Wrap the dough in plastic wrap and place in the fridge to chill for at least 1 hour. This is imperative.
Once you take out the dough, it should be hard to touch but it will be easier to mold once the heat of your hands come in contact.
Grab 1 tbsp size piece of dough and shape like a small ball and slightly flatten the top. Make sure it is smooth. Add 1 piece of pistachio or almond on top by gently pressing it down half way. Place on a parchment lined baking tray.
Keep repeating this step until there is no longer any dough. Make sure there is a few inches of space between the cookies.
Bake in a 350 F oven for 15-20 minutes max. The bottom should be lightly browned. Bake at the middle rack all throughout or the bottom rack for 15 min then the top rack for 5 minutes.
Allow the cookies to cool before touching or they can break. If they flatten a little bit, that is fine because it is a butter based cookie but in order to prevent flatenning; make sure the butter was room temp. to start with and the dough chilled properly.
Sprinkle some powedered sugar on top if you would like and enjoy!