Cream the softened unsalted butter and full-fat cream cheese with light brown sugar and granulated sugar in a stand mixer on medium speed for about 5 minutes until fluffy.

Add the large egg and pure vanilla extract. Mix on low speed until just combined.

Whisk together all-purpose flour, cornstarch, baking soda, and optional salt in a separate bowl. Gradually add to the wet ingredients on low speed until just combined.

Gently fold in the semi-sweet chocolate chips or chunks using a spatula.

Form mounds of dough using a cookie scoop, flatten slightly, cover with plastic wrap, and refrigerate for at least 2 hours.

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

Bake the chilled cookie mounds for 8-10 minutes until edges set and centers remain slightly glossy.

Allow cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack.