1-First Step: Prep and Preheat
Preheat your oven to 375°F (190°C). Line baking sheets with parchment paper or silicone mats to prevent sticking. Measure and prepare all ingredients for smooth assembly.

2-Second Step: Cream the Butter and Sugars
In a large mixing bowl, beat the cold cubed butter with dark brown sugar, light brown sugar, and granulated sugar on low speed for 30 seconds. Increase to medium speed and mix for about 4 minutes until the mixture is light and fluffy, forming the base for tender cookies.

3-Third Step: Add Eggs and Flavorings
Add eggs, vanilla extract, salt, baking soda, and optional cornstarch to the bowl. Beat on medium speed for about 1 minute until well combined and smooth, scraping the sides as needed to incorporate all ingredients evenly.

4-Fourth Step: Incorporate Flour
On low speed, gradually add the all-purpose flour. Mix just until combined to prevent overworking the dough, which can make cookies tough.

5-Fifth Step: Stir in Chocolate Chips and Walnuts
Fold in chocolate chips and chopped walnuts carefully by hand or on low mixer speed to evenly distribute without breaking the nuts excessively.

6-Sixth Step: Portion Dough
Use a large cookie scoop or about 3 tablespoons of dough per cookie and place on prepared baking sheets about 2 inches apart. Press extra chocolate chips or walnut pieces on top if desired for a pretty finish.

7-Seventh Step: Bake Cookies
Bake for 8 to 12 minutes until edges are lightly golden but centers remain soft. At 375°F, aim for 10-11 minutes. If baking at 400°F, stick closer to 8-9 minutes to avoid overbaking.

8-Final Step: Cool and Serve
Remove cookies from oven and let cool on baking sheets for 2-3 minutes to firm up before transferring to wire racks to cool completely. Optionally sprinkle flaky sea salt on warm cookies for a delightful sweet-salty contrast. Serve warm or store as desired.