Scoop 8-10 tablespoon-sized dollops of pistachio cream onto a parchment-lined plate. Freeze for at least 1 hour until totally solid.

In a mixer, beat the cold cubed butter, brown sugar, and granulated sugar for 2-3 minutes until fluffy.

Add the cold egg and vanilla extract, mixing until just combined.

Whisk together the flour, cornstarch, baking soda, and salt. Add to the wet ingredients and mix on low until a dough forms. Fold in the chocolate chunks.

Divide the dough into 8-10 portions. Flatten each into a disk. Place a frozen pistachio cream puck in the center of each disk and carefully seal the dough completely around it.

Chill the stuffed dough balls in the refrigerator for 30 minutes.

Preheat oven to 350°F (175°C). Place the chilled dough balls on a parchment-lined baking sheet, spaced 2 inches apart. Press extra chocolate chunks and chopped pistachios on top.

Bake for 11-13 minutes until the edges are golden. Sprinkle with flaky sea salt if desired.

Let cool on the baking sheet for 10 minutes before moving to a wire rack. Enjoy warm for a molten center.