Preheat oven to 350 degrees. Line 2 cookie sheets with parchment paper or a silicon liner.

In a heavy bottomed sauce pan, melt butter until browned. It takes about 5 minutes for butter to begin to smell nutty and start to brown, but watch carefully because it goes from perfectly browned to burned very fast.

Once browned, remove from heat and allow to cool for 5 minutes.

Combine flour, baking soda, and salt to a large bowl and set aside.

Combine browned butter and sugars to the bowl of your mixer and mix until combined.

Add egg and yolk one at a time then add the vanilla, mixing until completely incorporated.

With your mixer running on low, gradually add flour mixture; mixing until just combined.

Turn mixer off and mix in chocolate chunks with a spoon.

Refrigerate dough for at least 30 minutes.

Refrigerate Nutella for at least 30 minutes.

Once dough is cold, spoon a tablespoon of dough. Roll dough into a ball then flatten into a small disk.

Place a teaspoon of Nutella in the middle of the disk. Top with another disk shaped dough. Pinch sides together then carefully roll into a ball.

Place on a cookie sheet 3 inches apart (I usually only put 5 on a sheet)

Sprinkle balls with flaked sea salt (optional).

Bake cookies for 12-14 minutes, depending on your oven.