Preheat oven to 350°F. Line two baking sheets with parchment paper.
Beat butter, brown sugar, and granulated sugar until light and creamy.
Mix in yogurt, milk, and vanilla until smooth.
Whisk flour, cornstarch, baking soda, and salt in a separate bowl.
Add dry ingredients to the wet mixture. Stir just until a soft dough forms.
Fold in chocolate chips evenly throughout the dough.
Scoop heaping 1.5-tablespoon portions onto sheets, spacing about 2 inches apart.
Bake 10–12 minutes, until edges are set and centers look slightly underdone.
Cool on the sheet 5 minutes, then transfer to a rack to finish cooling.