Using either a hand or standing mixer with a paddle attachment, cream together the room temperature butter and sugar. Add the egg yolk, heavy cream, and vanilla extract, beating well until combined.

1/2 cup unsalted butter, 2/3 cup granulated sugar, 1 unbeaten egg yolk, 2 Tablespoon heavy cream, 1 tsp vanilla extract

Add the flour, baking powder, salt, and 1/2 cup chopped pistachios. Mix thoroughly.

1 cup all-purpose flour, 2 tsp baking powder, 1/2 tsp salt*

Place the cookie dough on a large piece of plastic wrap, and lightly flour your (clean) hands to prevent the dough from sticking too much. Shape dough into a log, approximately 12 inches long. Wrap the log of dough in the plastic wrap until covered and chill overnight in the fridge.

The next day, preheat the oven to 400°F. In a small bowl, stir together the remaining 2 tablespoons granulated sugar with the remaining 1/4 cup finely chopped pistachios; set aside.

Lightly beat the saved egg white and brush evenly onto the exterior of the dough log, coating it completely. Place the dough log on a baking sheet and pour the sugar-pistachio mixture on top of the log. Then, roll the log in the sugar mixture, pressing it into the dough as needed, until completely coated.

Use a sharp knife to cut the log into 1/4 inch slices. Place the slices on a baking sheet (I always use parchment-lined baking sheets), leaving approximately 2 inches of space between each cookie. Bake for 7-10 minutes, until slightly golden brown along the edges. Let the cookies rest for 1-2 minutes on the baking sheet, then transfer to a cooling rack. Once completely cooled, store in an airtight container at room temperature for 3-4 days.