1- Line a baking sheet with parchment paper. Scoop 15 one-tablespoon portions of Nutella onto the parchment, freeze for about one hour or until solid to prevent melting during baking.

2- Preheat oven to 350°F (175°C) and line a large baking sheet with parchment paper.

3- In a medium bowl, whisk together all-purpose flour, cornstarch, cocoa powder, baking soda, and salt.

4- In a large bowl, beat butter, granulated sugar, and brown sugar until smooth and lightened in color.

5- Add eggs one at a time, mixing in vanilla with the second egg; the mixture may separate slightly.

6- Gradually combine dry ingredients with the wet mixture until fully incorporated.

7- Scoop ¼ cup portions of cookie dough, flatten into roughly 4-inch disks.

8- Place one frozen Nutella ball in the center of each disk, then fold dough completely around it, rolling into a smooth ball ensuring no cracks.

9- Place 5-6 cookies on the baking sheet, spacing at least 3 inches apart.

10- Bake for 10-12 minutes until cookies spread and the surface loses its shiny appearance but centers remain soft.

11- Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

12- For the best molten effect, serve warm; optionally, sprinkle with flaky sea salt before serving.