First, freeze your chocolate hazelnut spread centers. Line a small cookie sheet or plate with parchment paper. Measure out 12 separate teaspoons of chocolate hazelnut spread and place spaced out onto the parchment paper. Place into the freezer. This can be done up to a day ahead. Make your cookie dough. Melt your butter, you can do this on the stove top or in a bowl in increments in the microwave. Stir in your 1/4 cup (74g) of chocolate hazelnut spread and cocoa powder until completely smooth and set aside.
In a large bowl, whisk together your light brown and granulated sugar and egg until thickened. Add in your vanilla and hazelnut extract and continue to mix together with speed until smooth. Note: if you don't have hazelnut extract, replace with additional vanilla. Pour your butter mixture into your egg mixture and use a whisk or spatula to combine completely.
Next, add in your dry ingredients - flour, baking soda and salt. Using a spatula, fold your dry ingredients in until a shaggy dough forms. Add in all of your chopped chocolate and continue to mix until your chocolate is evenly dispersed and your dough has formed. Place your dough into the fridge to chill uncovered until firm, about 1 to 2 hours. If it will be in the fridge longer, be sure to cover it.
Shape, bake and enjoy your cookies. Line a large cookie sheet and portion out your dough into 12 scoops, each weighing about 55-60 grams or 2 1/2 to 3 tablespoons in size. Flatten each dough scoop and then create a small bowl shape with each portion of dough. Remove your frozen chocolate hazelnut dollops from the freezer and with speed add one to the center of each cookie dough ball. Carefully, using your hands, reform your cookie scoops into a ball shape, leaving some chocolate hazelnut spread showing at the top.
Cover your shaped cookie dough balls with plastic wrap, and put your cookie sheet into the fridge to chill for 4 to 6 hours or overnight (up to 24 hours). When you're ready, preheat your oven to 350 degrees. Bake your cookies for 10 to 12 minutes. Remove from the oven and gently shape as needed using a round cookie cutter or bowl slightly larger than your cookies to nudge the edges in to create perfectly round cookies. There also may be a slight film that forms on top of your chocolate hazelnut spread center - you can leave this be, or if it bothers you, simply take a small utensil and gently mix the filling right when it's out of the oven and you'll see the smooth, glossy spread come to the top.
Allow your cookies to cool directly on the cookie sheet for at least 20-30 minutes - if you try to move them sooner you'll risk some breakage! Then dig in and enjoy. These cookies taste best when warm, enjoyed the same day you baked them. They will still taste delicious though if stored in an airtight container in the fridge for up to 5 days, and you can enjoy cold or warmed up. If you'd like, you can also bake these cookies and then freeze them to enjoy at a later time.