In the bowl of a stand mixer, beat together the butter, Nutella, brown sugar & white sugar with the paddle attachment until combined and creamy, about 2 minutes. Beat in the egg and vanilla to combine. Lastly, beat in the flour, cornstarch, baking soda and salt until a soft dough has formed. Stir in the chopped hazelnuts and the white chocolate chips.

Refrigerate the dough for AT LEAST 2 hours, if not overnight. Once the dough has chilled for at least 2 hours, preheat your oven to 350 degrees F. Line 2 baking sheets with silicone liners or mist them lightly with cooking spray.

Portion heaping 1/4-cup sized balls of dough onto the baking sheets, about 2" apart. Bake for approx. 8-10 minutes, rotating pans halfway through baking time to ensure even cooking. I cooked mine for exactly 9 minutes; do not over-bake. Cookies may appear slightly underdone but that's okay as they will continue to set up as they cool. Allow the cookies to cool on the baking sheets completely, then transfer to a wire rack. Serve! Store leftovers in an airtight container at room temperature. Store leftover hazelnuts in the freezer to preserve freshness.