Scoop the chocolate filling. Scoop the Nutella by the teaspoon onto a parchment-lined tray. Chill in the freezer until frozen solid, about 20-30 minutes.
Whisk the sugar and butter. Whisk the sugar and brown sugar into the melted butter vigorously for 1 minute until combined.
Mix in the wet ingredients. Whisk in the egg and vanilla extract.
Mix in the dry ingredients. Fold in the flour, baking soda, and salt until almost combined, then fold in the chopped chocolate. Cover and chill the bowl in the fridge for 30 minutes.
Scoop the cookie dough. Scoop dough with a 2-tablespoon cookie scoop, flatten, add frozen chocolate filling, seal, and roll into a round shape.
Chill the stuffed cookies. Place the cookie dough balls on a parchment-lined baking sheet. Freeze until frozen solid, about 1-2 hours minimum. Then preheat the oven to 350 F/180 C.
Bake! Bake the cookies spaced 2 inches apart for 10-12 minutes or until the edges are golden brown and the middle is puffy but still pale and underbaked. Let the pan cool on a wire rack for about 15-20 minutes, then remove and enjoy!
Store baked chocolate filled cookies in an airtight container at room temperature for 2-3 days. The filled cookie dough balls can be frozen and stored in an airtight container or freezer bag for up to 3 months.