original recipe with pictures here: http://thetummytrain.com/2014/06/10/what-could-be-better-than-a-chocolate-chip-cookie/

2 ¼ cups all purpose flour
1 ¼ teaspoons baking soda
¼ teaspoon salt
1 cup unsalted butter
1 ¼ cups packed dark brown sugar
¼ cup white sugar
1 large egg + 1 egg yolk
1 ½ teaspoons vanilla extract
1 tablespoon plain Greek yogurt *
2 cups semi-sweet or dark chocolate chips
1 jar of Nutella, chilled in the refrigerator (you will use approximately 36 Tablespoons)
Coarse sea salt, for sprinkling

2 ¼ cups all purpose flour 1 ¼ teaspoons baking soda 1 cup unsalted butter 1 ¼ cups packed dark brown sugar 1 large egg + 1 egg yolk 1 ½ teaspoons vanilla extract 1 tablespoon plain Greek yogurt * 2 cup s semi-sweet or dark chocolate chips 1 jar of Nutella, chilled in the refrigerator (you will use approximately 36 Tablespoons)

1. Whisk together the flour, baking soda, and salt in a bowl and set aside.
2. Melt butter in a saucepan over medium heat. The butter will begin to foam. Make sure you whisk consistently during this process.

3. After a few of minutes of constant whisking, the butter will begin to darken on the bottom of the saucepan. As soon as the butter has turned brown and gives off a nutty aroma, remove the pan from the heat and continue to whisk as it is transferred to a bowl to prevent burning. Set aside to cool for a few minutes.

4. With an electric mixer fitted with the paddle attachment, mix the butter and sugars until thoroughly blended. Beat in the egg, yolk, vanilla, and yogurt until combined.

5. Add the dry ingredients slowly and beat on low-speed (or using a spatula) just until combined. Gently fold in all of the chocolate chips.

6. Chill dough for 2 hours in the refrigerator. Meanwhile, line two baking sheets with parchment paper. In the last 20 minutes of chilling, preheat the oven to 350°F (180°C).
7. Once dough is chilled, measure about 1 and 1/2 tablespoons of dough and roll into a ball. Flatten the dough ball very thinly into the palm of your hand. Place 1 teaspoon of chilled Nutella in the middle and fold dough around it; gently rolling into a ball — it doesn’t have to be perfectly rolled! Make sure that the Nutella is not seeping out of the dough. Add more dough if necessary.

8. Place dough balls on cookie sheet 2 inches apart, then flatten just a little bit with a very gentle hand to even the tops. Bake the cookies 9 to 11 minutes or until the edges of the cookies begin to turn golden brown. They will look a bit underdone in the middle, but will continue to cook once out of the oven.

9. Cool the cookies on the sheets for at least 2 minutes. Sprinkle with a little sea salt. Transfer cookies to a wire rack to cool completely.