With the paddle attachment on a stand mixer or with a hand-held electric mixer, beat the room-temperature butter and both sugars on medium-high speed until light and fluffy, about 2 to 3 minutes.

Scrape down the sides and bottom of the bowl. Add the eggs and vanilla and beat on low until well combined, about 1 minute.

Add the flour, cornstarch, baking soda, and salt. Mix on low speed just until the dry ingredients are incorporated, scraping the bowl as needed. Do not overmix.

Break the mini pretzels into pieces. Keep the Nutella chips in the freezer until just before using. With the mixer on low, add the pretzel pieces and the frozen Nutella chips and mix just until evenly distributed.

Transfer the dough to the freezer for 15 minutes to firm up so it is easier to scoop.

After 15 minutes, scoop the dough into 2-ounce portions (about 2 inches) and roll each into a ball. Place the balls on a tray lined with parchment paper (they may touch). Cover the tray with plastic wrap and refrigerate the dough balls for at least 3 hours or up to overnight.

When ready to bake, preheat the oven to 350°F (177°C). Line cookie sheets with parchment paper or silicone baking mats. Arrange up to 8 cookie balls per sheet, spacing them to allow for spreading.

Bake for 10 to 12 minutes, or until the edges are set and the tops are golden.

Let the cookies cool on the baking sheet for about 5 minutes, then transfer to a wire rack to cool completely.