Preheat oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a large bowl, whisk together melted butter, brown sugar, and granulated sugar until smooth and glossy.

Add eggs and vanilla extract, whisking until fully combined.

In a separate bowl, mix oats, flour, baking soda, and salt.

Gently fold dry ingredients into the wet mixture until just combined — do not overmix.

Fold in chopped chocolate, then swirl in pistachio cream, leaving visible streaks.

Scoop dough onto prepared baking sheets, spacing cookies about 2½ inches apart.

Optional: Chill dough for 20–30 minutes for thicker cookies.

Bake for 10–13 minutes, until edges are set and centers still look soft.

Let cookies cool on the baking sheet for 10 minutes before transferring to a rack.