In a stand mixer fitted with the paddle attachment (or in a large bowl with an electric mixer), cream the softened butter, brown sugar, and granulated sugar on medium-high until light and well combined, about 4 minutes.
Add the egg and vanilla and beat until incorporated, scraping down the bowl as needed.
On low speed, add the all-purpose flour, cornstarch, baking soda, and optional pinch of salt, and mix until just combined, about 1 minute.
Add the mini pretzel twists and chocolate chips; mix on low until evenly distributed and the pretzels are broken to your desired size, about 1 minute (you can crush pretzels by hand before adding if you prefer smaller pieces).
Use a large cookie scoop, 1/4-cup measure, or your hands to form 10 equal mounds of dough; roll into balls and flatten slightly.
Place the dough mounds on a plate or tray, cover with plastic wrap, and refrigerate for at least 2 hours and up to 3 days; chilling prevents spreading.
Preheat the oven to 350°F (177°C). Line a baking sheet with a Silpat or parchment paper or spray with cooking spray.
Arrange the chilled dough mounds on the prepared baking sheet at least 2 inches apart (about 8 per sheet) and optionally press a few extra pretzel pieces and chocolate chips on top, keeping larger pretzel pieces off direct contact with the sheet to avoid burning.
Bake for about 10 to 12 minutes, until the edges are set and the centers are just set and still slightly glossy; do not overbake.
Let the cookies cool on the baking sheet for about 10 minutes before serving.