01 -
Preheat the oven to 350°F (175°C). Line baking sheets with parchment paper.
02 -
In a large mixing bowl, beat together the softened butter, light brown sugar, and granulated sugar until the mixture is light and fluffy.
03 -
Add in the egg and vanilla extract; beat until thoroughly combined with the creamed mixture.
04 -
Add the all-purpose flour, cornstarch, baking powder, baking soda, and salt to the wet ingredients. Mix until just combined, careful not to overwork the dough.
05 -
Gently fold in the semi-sweet chocolate chips and walnut pieces, if using, ensuring even distribution throughout the dough.
06 -
Scoop the dough into portions of approximately 2 tablespoons each and place on the prepared sheets. For thicker cookies, chill the tray of dough balls for 30 minutes before baking.
07 -
Bake in batches for 9 to 11 minutes, until edges are lightly golden but centers remain visibly under-baked for a gooey texture.
08 -
Allow cookies to rest on the baking sheet for 5 minutes to finish setting, then transfer to a wire rack to cool completely.