Preheat oven to 350°F.
Spread a piece of parchment paper out on a large baking sheet. Using a ½-tablespoon measuring spoon, measure out heaping scoops of Nutella, and place them on the baking sheet. You should have 24 total scoops. Place the baking sheet in the freezer for at least 20 minutes, until the Nutella hardens.
1 cup Nutella
While the Nutella chills, in a large bowl, cream the butter and sugars together using a hand mixer. Beat in the egg and vanilla extract until incorporated.
½ cup unsalted butter, ½ cup brown sugar, ¼ cup granulated sugar, 1 large egg, 1 teaspoon pure vanilla extract
In a separate bowl, whisk together the flour, baking soda, and salt. Add the flour mixture to the wet ingredients, little by little, beating lightly after each addition. Stir the chopped dark chocolate into the batter.
2 cups all-purpose flour, ½ teaspoon baking soda, ½ teaspoon kosher salt, 3 ounces finely chopped dark chocolate
Remove the Nutella from the freezer. Use a cookie scoop to gather a portion of the dough in your hand. Make a small indentation in the ball of dough. Take a frozen dollop of Nutella and place it in the well of the cookie dough, and gently roll the dough between your hands to form a ball that completely covers the Nutella. Place back on the baking sheet. Repeat until the cookie dough is gone.
Place the cookie dough balls in the refrigerator for 5 minutes.
Bake for 10-12 minutes, then let cool on a wire rack.