Chocolate hazelnut spread (such as Nutella), about ½ cup
1 cup (16 tbsp.) unsalted butter
2¼ cups all-purpose flour
1¼ tsp. baking soda
½ tsp. coarse sea salt, plus more sprinkling
1 cup light brown sugar
½ cup granulated sugar
1 large egg plus 1 egg yolk
2½ tsp. vanilla extract
1 tbsp. greek yogurt or sour cream
1 cup semisweet chocolate chips
¾ cup dark chocolate chips
Line a baking sheet with wax or parchment paper. Pipe small dollops of chocolate hazelnut spread unto the wax paper, about 1-1½ teaspoons each. You will need about 2 dozen. Transfer the baking sheet to the freezer and let sit until firm, about 2 hours.
Melt the butter in a skillet over medium heat. Continue to cook, whisking frequently, until the butter foams, bubbles slightly, and begins to brown. Remove from the heat and let cool.
Whisk together the flour, baking soda and salt.
In another bowl cream the sugars and the brown butter. Mix on medium speed until well blended and smooth. Blend in the egg and egg yolk, scraping down the bowl as needed. Blend in the vanilla and greek yogurt. Reduce the mixer to low speed, blend in the dry ingredients just until incorporated. Fold in the chocolate chips. Chill the dough briefly, about 30 minutes.
Preheat the oven to 350˚ F. Use a medium dough scoop (about 2 tablespoons) to scoop a portion of cookie dough. Press an indentation into the center of the dough ball to create a bowl shape. Place a dollop of the frozen Nutella in the indentation and pinch together the edges of the cookie dough over the top to completely seal it in the center.
Transfer the shaped cookies on prepared baking sheets, 2-3 inches apart. Bake until the cookies are golden brown and set, rotating the pans halfway through, about 14 minutes total.
When the cookies are finished baking, sprinkle lightly with additional sea salt. Let sit a few minutes, then transfer to a wire rack to cool. Repeat with the remaining dough as needed.
*Be sure to replace the remaining Nutella dollops in the freezer while waiting for cookies to bake. It softens fairly quickly otherwise.