Combine butter, cream cheese, sugars, egg, and vanilla in a stand mixer and beat on medium-high speed until light and fluffy, about 5 minutes.

Scrape down the sides of the bowl and add flour, cornstarch, baking soda, and optional salt. Mix until just combined, about 1 minute.

Add chocolate chips and chunks and incorporate by folding or momentarily beating.

Using a 2-inch cookie scoop, form mounds and place on a plate. Flatten slightly, cover with plastic wrap, and refrigerate for at least 2 hours.

Preheat oven to 350F, line a baking sheet with a baking mat or spray with cooking spray. Place mounds on the sheet, spaced 2 inches apart.

Bake for 8 to 9 minutes, until edges are set and tops are beginning to set. Do not bake longer than 10 minutes.

Cool cookies on the baking sheet for 5 minutes before transferring to a rack.

Store airtight at room temperature for up to 1 week or freeze for up to 3 months.