In a large mixing bowl or stand mixer, combine softened unsalted butter and cream cheese. Beat on medium speed until light and fluffy, about 2-3 minutes. Gradually add light brown sugar and granulated sugar, mixing until well incorporated.

Add a large room-temperature egg and pure vanilla extract to the creamed mixture. Mix on low speed until combined, about 1 minute.

In a separate bowl, whisk together all-purpose flour, cornstarch, baking soda, and optional salt. Gradually add the dry mixture to the wet ingredients, mixing on low speed just until no dry streaks remain. Avoid overmixing.

Gently fold in semi-sweet chocolate chips or chunks with a spatula until evenly dispersed.

Cover the bowl and refrigerate for at least 2 hours and up to 5 days.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper. Scoop tablespoons of dough onto prepared sheets, spaced about 2 inches apart. Bake for 8-10 minutes.

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