Line two large baking sheets with a silicone mat or parchment paper, then set aside.

In a medium bowl, sift or whisk together the 2 ¾ cups flour, cornstarch, baking powder, baking soda, and salt. Set aside.

In a standing mixer fitted with a paddle attachment, beat the on low butter until it comes together and becomes creamy, about 1 minute. Add in the sugars and beat for another 2-3 minutes, until the butter and sugar become homogeneous.

Mix in the eggs and vanilla and beat on medium low speed until just incorporated. Gradually add in the flour mixture, about ½ cup at a time, mixing until only a small amount of unincorporated flour remains.

In a medium bowl, toss the 2 tablespoon flour with the walnuts and the chocolate chips until they are coated in the flour. Fold the chocolate chips and walnuts into the dough by hand with a wooden spoon or rubber spatula, making sure to distribute the ingredients evenly throughout the dough.

Using an ice cream scoop, scoop out the dough and place each cookie onto the prepared baking sheets, 2 inches apart. Refrigerate for at least one hour but up to 12 hours before baking.

Preheat oven to 375°F.

Bake cookies for 13-15 minutes, until light golden brown. Do not over bake; the cookies will continue to cook as they cool.

Cool on a wire rack until manageable, then serve warm.