Preheat oven to 350°F and line 2 large baking sheets with parchment paper.
Place flour, baking powder, baking soda, cornstarch, and salt in a large bowl and whisk to combine.
Place softened butter and brown sugar in an electric mixer fitted with the paddle attachment and beat until fluffy.
Add the sweetened condensed milk and vanilla extract to the bowl and beat until thoroughly combined.
Add the dry ingredients to the bowl and stir until the cookie dough forms. Add the chocolate chips and gently stir until the chips are incorporated throughout the dough.
Using a small scoop or tablespoon measure, portion the dough, and transfer to the prepared baking sheet, placing each portion approximately 2-inches apart.
Gently flatten each cookie dough portion into a puck and place in the oven.
Bake for 10-12 minutes or until the cookies are just golden around the edges. Remove from the oven and set aside to cool on a wire rack.