Freeze 12 small dollops of Nutella on a parchment-lined tray for at least 30 minutes.
Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper.
Cream together the butter, brown sugar, and granulated sugar until fluffy.
Add eggs and vanilla extract, and mix until smooth.
Stir in flour, baking soda, and salt just until combined.
Fold in the mini marshmallows gently.
Scoop dough into balls, flatten each slightly, and place a frozen Nutella dollop in the center.
Wrap the dough around the Nutella and roll into a ball.
Bake for 10–12 minutes, or until edges are golden and marshmallows are slightly toasted.
Cool for 5 minutes before transferring to a wire rack.