Preheat your oven to 350°F (175°C).

In a large mixing bowl, cream together unsalted butter, brown sugar, and granulated sugar until light and fluffy, about 3-4 minutes. Incorporate the egg and mix well. Gradually add flour, baking soda, and salt, mixing just until incorporated.

Scoop out about 2 tablespoons of dough, flatten gently, place a dollop of pistachio cream, enclose it, and roll into a ball.

Line a baking sheet with parchment paper, arrange cookie balls, and bake for 10-12 minutes until edges are golden but centers are slightly underbaked.

Let cool on the baking sheet for about 5 minutes before transferring to a wire rack to cool completely.