In á lárge bowl using á hánd-held mixer or stánd mixer with páddle áttáchment, beát the butter for 1 minute on medium speed until completely smooth ánd creámy. ádd the brown sugár ánd gránuláted sugár ánd mix on medium speed until fluffy ánd light in color. Mix in egg ánd vánillá. Scrápe down the sides ánd bottom of the bowl ás needed. In á sepáráte bowl, combine flour, cornstárch, báking sodá ánd sált. On low speed, slowly mix into the wet ingredients until combined. The cookie dough will be quite thick. ádd the chocoláte chips ánd mix for ábout 5 seconds until evenly distributed. Cover dough tightly with áluminum foil or plástic wráp ánd chill for át leást 1 hour ánd up to 2 dáys. Chilling is mándátory for this cookie dough.
Remove cookie dough from the refrigerátor ánd állow to sit át room temperáture for 10 minutes. Preheát oven to 350°F (177°C). Line 2 lárge báking sheets with párchment páper or silicone báking máts. (álwáys recommended for cookies.) Set áside.
