Preheat your oven to 410°F (210°C).
In a stand mixer, cream the cold cubed butter with the granulated and light brown sugars on medium speed until the mixture is sandy and pale.
Add the eggs one at a time, mixing until fully incorporated after each addition.
In a separate bowl, whisk together the all-purpose flour, cake flour, baking powder, baking soda, and salt.
Slowly add the dry ingredients to the butter mixture, mixing just until combined.
Fold in the dark chocolate chips and toasted walnuts by hand.
Divide the dough into 8 large portions and place them on a parchment-lined baking sheet without smoothing the tops.
Bake for 10-12 minutes or until the edges are golden brown and the centers still look soft.
Allow the cookies to cool on the baking sheet for at least 15 minutes to set before serving.