Wash your hands. Beat butter in a large bowl until creamy. Add egg white and continue blending. Add dry sugar cookie mix and mix with hands or mixer until dough is formed.
Place pistachios in a Ziploc bag, removing air before sealing. Roll over the bag with a rolling pin to crush the nuts. Add 1/3 cup of the pistachios to the dough and use hands to knead until fully incorporated. Reserve the remaining nuts for topping.
Gather dough into a ball and flatten into a square shape. Cover with plastic wrap and freeze for 20 minutes or until dough is firm. While dough is chilling, preheat oven to 350 degrees.
Remove dough from freezer. Lightly flour your countertop and rolling pin. Roll out the dough until its approximately 1/8” to 1/4” thick.
Use a pizza cutter to cut the dough into 2 ½“ squares, until you have approx. 20 cookies. Place squares on parchment-lined cookie sheets and bake for 13-15 minutes or until edges are golden.
Once cookies have cooled, microwave chocolate in 10 second increments until fully melted. Dip cookies into melted chocolate and place onto parchment-lined baking sheet. Sprinkle with remaining crushed pistachios before chocolate hardens.