Cream together ½ cup of unsalted butter and ⅔ cup of granulated sugar until light and fluffy, about 3 minutes. Add the egg yolk, heavy cream, and vanilla extract, stirring until smooth.

In another bowl, whisk together the flour, baking powder, and salt. Gradually integrate into the wet mixture, mixing on low speed until combined. Fold in the finely chopped pistachios.

Shape the dough into a log about 12 inches long and wrap in plastic wrap. Refrigerate overnight.

Preheat your oven to 400°F (204°C) the next day.

Mix the remaining sugar and ¼ cup of chopped pistachios for coating in a small bowl.

After chilling, brush the log with the reserved egg white. Roll in the sugar-pistachio mixture to coat.

Slice the log into ¼-inch rounds and place them on a parchment-lined baking sheet. Bake for 7-10 minutes until edges are lightly golden.