To the bowl of a stand mixer fitted with the paddle attachment (or large mixing bowl and electric mixer) add the butter, Nutella, sugars, egg, vanilla, and beat on medium-high speed until creamed and well combined, about 4 minutes.
Stop, scrape down the sides of the bowl, and add the flour, cornstarch, baking soda, optional salt, and beat on low speed until just combined, about 1 minute.
Stop, scrape down the sides of the bowl, and add the chocolate chips, and beat on low speed until just combined, about 30 seconds.
Using a large cookie scoop, 1/4-cup measure, or your hands, form approximately 16 equal-sized mounds of dough, roll into balls, and flatten slightly. Tip – Strategically place a few chocolate chips on top of each mound of dough by taking chips from the underside and adding them on top.
Place mounds on a large plate or tray, cover with plasticwrap, and refrigerate for at least 3 hours, up to 5 days. Do not bake with unchilled dough because cookies will bake thinner, flatter, and be more prone to spreading.
Preheat oven to 350F, line a baking sheet with a Silpat or spray with cooking spray. Place dough mounds on baking sheet, spaced at least 2 inches apart (I bake 8 cookies per sheet).
Bake for about 9 to 10 minutes, or until edges have set and tops are just set, even if slightly undercooked and glossy in the center; don’t overbake. Cookies firm up as they cool.
Allow cookies to cool on baking sheet for about 10 minutes before serving. I let them cool on the baking sheet and don’t use a rack.
Notes
Storage: Cookies will keep airtight at room temperature for up to 1 week or in the freezer for up to 6 months. Alternatively, unbaked cookie dough can be stored in an airtight container in the refrigerator for up to 5 days, or in the freezer for up to 4 months, so consider baking only as many cookies as desired and save the remaining dough to be baked in the future when desired.Adapted from Soft and Chewy Nutella White Chocolate Chip Cookies.