Optional Step: Blanche chopped pistachios for 30-60 seconds by covering with boiling hot water in a small bowl. Strain well and set aside.
Cream butter and sugar together on low speed in a stand mixer bowl with the paddle attachment for about 1 minute to combine.
Mix almond extract in for about 20 seconds, then flour and salt and run until a dough forms (about 1 minute).
Using the mixer or by hand add pistachios to the dough (if using the mixer, stop as soon as incorporated).
On a lightly floured surface, roll dough into a ball, then into a log (about 2 inches in diameter), cover tightly in plastic wrap and chill for at least 2 hours (I often do overnight).
When ready to bake, preheat oven to 325F and line a baking sheet with parchment paper.
With a sharp knife, slice ½ ” cookies and place them on prepared sheet with some space between (they will not spread too much).
Bake for 10 minutes or until the edges just start to look set, the tops will still look shimmery.
Chill on the cookie sheet for about 10 minutes before transferring to a wire rack to cool completely.
If topping, melt chocolate in a heat-safe bowl in the microwave, incrementally, mixing in between.
Carefully place melted chocolate into a piping bag, cut a small hole in the tip and drizzle as desired. Sprinkle with pistachios.