Start by lining a s small baking sheet or plate with parchment paper.After stirring the Nutella jar vigorously, use a measuring teaspoon to drop 11 dollops of Nutella on the parchment paper. Make sure to leave enough space between each dollop so they don't merge together. Place in the freezer.
While the Nutella is in the freezer, make the cookie dough.
In a medium bowl, cream the butter and both sugars together. Add in the vanilla and the egg yolk and mix again until smooth.
Add in the dry ingredients (flour, cornstarch, baking soda, salt) over the wet ingredient mixture. Stir just until combined then fold in the chocolate chips.
Using a small cookie scooper, scoop out 11 equally sized cookie dough balls placing each one on a parchment lined baking sheet.
Time to fill the cookies with Nutella!
To fill the chocolate chip cookies with Nutella, grad one cookie dough ball and flatten it between the palm of your hand, grab one dollop of Nutella from the freezer, place it in the middle and gently for the edges of the cookie inwards, seal it and roll the cookie dough between the palm of your hands and place the cookie dough ball back on the baking sheet. Repeat the process with all the cookies making sure to pull out the Nutella dollops as you go, because they melt very fast!
Place the cookies in the freezer for 30 minutes. While the cookies are chilling, preheat the oven to 350F.
After the cookies chilled for 30 minutes, bake them for 12-14 minutes or until the edges start looking a little golden brown and the centers is still pale. The cookies might look under baked but don't worry! They will continue baking as they cool down.
When the cookies are out of the oven make sure to. let them chill in the baking sheet for 15 minutes and then transfer them onto a cooling wrack.
You can store these Nutella stuffed chocolate chip cookies in an airtight container at room temperature for up to a week!