Place 14 teaspoons of Nutella onto a baking tray lined with parchment paper. Freeze until solid - about 1 hour.
Preheat the oven to 180C/350F/Gas 4, and line a baking tray with parchment paper, or a silicone mat. Set aside.
Whisk together the flour, baking powder, baking soda, cornflour, and salt. Set aside.
Whisk together the melted butter and sugars until combined. Add the egg and vanilla, and mix until combined.
Add the dry ingredients, and mix until just combined. Fold in the chocolate chips.
Roll the dough into 2oz balls. Form the balls into flat circles, and place 1 teaspoon of frozen Nutella into the centres. Form the dough back into balls, sealing the Nutella inside.
Place onto the prepared baking tray, and freeze for 1 hour (optional but results in thicker cookies). Bake for 12 - 14 minutes.
Allow to cool on the baking tray for 10 - 15 minutes before transferring to a wire rack to cool completely.
Video
Notes
These cookies are very soft and delicate the day they are baked due to the Nutella centre. Allow to set overnight for firmer cookies. (The cookies pictured were refrigerated overnight and left to come to room temperature the next day.)Cookies stay fresh, kept in an airtight container, at room temperature for up to 1 week. Cookie dough balls can be kept in the fridge for up to 5 days, or frozen for up to 3 months. Bake from frozen.