In a medium bowl, whisk together the flour, cornstarch, baking powder, and salt; set aside.
In a separate large mixing bowl, cream together the cream cheese, unsalted butter, and sugar until light and fluffy. Add the eggs, milk, and vanilla and mix until smooth.
Add the flour mixture to the cream cheese mixture and mix until no dry streaks remain. If using chocolate chips, stir in them. Cover and chill the dough for at least 1 hour.
Preheat the oven to 350°F (180°C) or 160°C for a fan oven. Line sheet trays with parchment paper and set aside.
Scoop the dough and roll it into golf ball-sized balls. Place them on the prepared trays at least 3” apart. If the dough is too soft to roll in your hands, scoop it and chill the dough balls on the sheet pan for 15 minutes, then try again.
Bake in the preheated oven for 10-12 minutes, or until lightly golden and no longer wet on top. Check doneness with a toothpick and allow to cool for 10 minutes on the pan before transferring to a wire rack to cool completely.
Sprinkle them with powdered sugar and serve immediately.
Notes
Use Room Temperature Ingredients: It's key that the eggs, butter, and cream cheese are all at room temperature before you start mixing the dough. This allows the ingredients to combine more smoothly and easily.
Chilling the Dough: Give the cookie dough at least an hour to chill in the fridge, or chill it overnight if that's more convenient. If the dough is too soft or sticky to handle, pop it back in the fridge for a bit and try again.
Checking for Doneness: You'll know that your cheesecake cookies are ready to come out of the oven when the tops of the cookies no longer look wet or sticky. Avoid baking these too long, as they can turn dry if they are overbaked.