Preheat your oven to 350°F (175°C). Spread the chopped walnuts on a baking sheet in an even layer and toast them for 8-10 minutes, keeping a close eye.

In a large mixing bowl, combine the softened unsalted butter with brown sugar and granulated sugar. Beat on medium speed for 2-3 minutes until light and fluffy.

Add one large egg and one egg yolk along with the vanilla extract to the creamed mixture. Mix on medium speed until smooth.

In a separate bowl, whisk together the flour, cornstarch, baking soda, and salt.

Gradually add the dry ingredients to the wet mixture and stir gently until a soft dough forms.

Fold in the chocolate chips and toasted walnuts until evenly distributed.

Scoop out the dough onto a tray lined with parchment paper, cover with plastic wrap, and chill in the refrigerator for at least 30 minutes.

Preheat your oven to 350°F (175°C) during chilling. Line two baking sheets with parchment paper.

Place six cookie dough balls on each baking sheet, allowing space for spreading. Bake for 11-13 minutes until edges are light golden brown.

Allow the cookies to cool on the baking sheet for about 5 minutes before transferring to a wire rack.