Chill The Nutella In Advance:

1. Scoop Nutella into 1/2 tablespoon balls onto a baking sheet lined with parchment and refrigerate or freeze.
2. Chill at least 3 hours or freeze for at least 30 minutes, to allow Nutella to harden. (This will make it easier to stuff into the cookies)

Next, Make Your Cookie Dough:

1. Brown & Cool The Butter. Melt the butter in a light-colored saucepan over medium heat, whisking constantly until the butter begins to foam. (Watch carefully when the butter begins to foam, as it will turn golden and brown quickly.) When the butter under the foam is golden (like honey) and smells sweet, remove the pan from the heat and transfer to the bowl of your stand mixer or a mixing bowl to cool for a few minutes, until it’s no longer hot to the touch.
2. Combine Brown Butter & Sugar. When the butter has cooled for a few minutes, add the sugar and brown sugar. Mix with the paddle attachment on medium speed 2-3 minutes or until well combined and the mixture looks like wet sand.
3. Add Eggs + Egg Yolk One At A Time. Add eggs + egg yolk one at a time, blending well after each addition.
4. Mix In The Vanilla. Add the vanilla and mix to combine.
5. Add Dry Ingredients. Add flour, cornstarch, baking soda, baking powder, and salt. Mix for a few seconds (it won’t be fully combined), then add the chocolate chips. Mix until just combined.
6. Scoop & Chill The Dough. Use a large cookie scoop (3 Tablespoon size) to scoop cookie dough balls. Place in an airtight container, cover, and chill the cookie dough balls for at least 2 hours, up to 1 day in advance.

Stuff & Bake The Cookies:

1. Preheat The Oven & Prep Your Pans. When you’re ready to bake, remove the dough from the refrigerator while the oven fully preheats to 350 degrees F. Line two baking sheets with parchment (so you can alternate sheets between batches.)
2. Stuff Cookies With Nutella. To fill the cookies with Nutella, break each cookie dough ball in half (I make one half slightly larger than the other and use that for the bottom.) Flatten the dough into a circle with your fingers, then add a chilled ball of Nutella in the center. Flatten out the other half of your cookie dough ball into a disc and cover the Nutella. Use your hands to gently seal the ball and make it smooth again. (See video for a visual, if needed.) Repeat with other cookie dough balls.
3. Bake & Cool The Cookies. Place 6 stuffed cookie dough balls onto a prepared baking sheet and bake at 350 degrees for 8-10 minutes, or until the edges are golden and the centers look just underdone. Cool on the baking sheet for 2 minutes before transferring to a cooling rack to finish cooling. Repeat process with remaining cookie dough.
4. Make Them Pretty! If desired, you can add flaky sea salt and a few extra chocolate chips to the cookies right after the come out of the oven.