Heat your oven to 410°F (210°C). Line a baking sheet with parchment paper to prevent sticking.
In a stand mixer (or using a hand mixer), beat the cold cubed butter, brown sugar, and granulated sugar until light and fluffy. This step helps aerate the dough for that signature thick texture.
Mix in the eggs one at a time, followed by the vanilla extract, until fully combined.
In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. Gradually add this to the wet mixture, mixing only until just combined.
Gently fold in the chocolate chips and chopped walnuts. Make sure they’re evenly distributed throughout the dough.
Using about ½ cup of dough per cookie, form large, rough balls. Place only 4 cookies per baking sheet to give them room to spread.
Bake for 10–12 minutes, until the edges turn golden brown but the centers remain soft. Don’t overbake—the cookies will continue cooking as they cool.
Let cookies cool for 5 minutes on the baking sheet before transferring to a wire rack. Serve warm for the ultimate gooey experience.
