In a large bowl using an electric mixer or in a stand mixer, cream together butter, cream cheese, brown sugar, and granulated sugar until light, fluffy, and well-combined.
Add egg and vanilla extract and stir to combine.
In a separate, medium-sized bowl, whisk together flour, cornstarch, baking powder, and salt.
With mixer on low-speed, gradually add flour mixture to butter/cream cheese mixture until completely combined. Scrape down sides and bottom of bowl as needed to ensure ingredients are well-combined.
Cover bowl with plastic wrap and transfer to the refrigerator to chill for at least two hours and up to 5 days.
Once dough has chilled and you are about ready to bake your cookies, preheat oven to 350F (175C).
Scoop cookie dough by 1 ½ Tablespoon-sized scoop and roll between your palms to form a smooth ball. Roll through granulated sugar (or other topping, if using) and place cookies 2” apart on parchment paper lined baking sheets.
Transfer to 350F (175C) preheated oven and bake for 13-14 minutes. Allow to cool completely on baking sheet before enjoying.
¹Take care to not over-measure your flour or your cookies will be cakey. Use a scale or stir your flour, scoop it into your measuring cup, and level it. Click the “flour” link in the ingredients for more information on how to properly measure flour.²I usually roll my cookies through granulated sugar, but other fun topping options are sprinkles (I love non-pareils) or a mix of ¼ cup granulated sugar and 1-2 teaspoons cinnamon.Place cookie dough back in the refrigerator between trays so it doesn’t become too warm. Never place cookie dough on a warm baking sheet.