Preheat your oven to 350F and line a large cookie pan with parchment paper.
In a food processor, place the toasted pistachios and process until finely ground.
Add the flour and sugar and process for about 15 seconds.
Process the butter until you don't notice any butter pieces, and have a mixture slightly moist, kind of like wet sand. About 15 seconds.
Add the yolk and milk and process until a soft dough is formed that easily pressed but does not stick.
Divide the dough into two, and roll each piece into a 1/3-inch thick over a large piece of parchment paper.
Remove dough from the refrigerator and use 2-2.5-inches round ridges cookie cutter to cut the dough.
Place the cut cookies over a larhe baking sheet lined with parchment paper.
Use a 1-inch round cookie cutter to cut half of the cookies at the center. ( I use a large piping tip)
Bake for 15-18 minutes, until the cookies are slightly puffy and very lightly browned.
Remove from the oven and allow the cookies to completely chill before you invert them.