Preheat oven to 350°F. Line two baking sheets with parchment.
Cream softened butter, granulated sugar, and brown sugar until light and fluffy, about 2 minutes.
Beat in eggs and vanilla until smooth, scraping the bowl once.
Whisk flour, baking soda, salt, and cornstarch in a separate bowl.
Add dry ingredients to the wet mixture on low speed just until combined.
Fold in white chocolate chips by hand until evenly dispersed.
Scoop dough into 1.5-tbsp mounds and set 2 inches apart on sheets.
Bake 9–11 minutes, until edges are set and centers look slightly pale.
Cool 5 minutes on the sheet, then transfer to a rack to finish cooling.