Line two large baking sheets with parchment paper. In a medium bowl, whisk together flours, baking powder, baking soda, and kosher salt.

In a large bowl using a hand mixer (or in the bowl of a stand mixer), cream cold butter on low speed until cubes lose half their shape, about 30 to 45 seconds. Add sugars and continue to cream briefly, 30 to 60 seconds more. Add chocolate and walnuts and beat until combined.

Gradually add flour mixture and beat to combine; mixture will be a bit crumbly. If any big pieces of butter remain, use hands to cut butter into smaller pieces. Add in eggs and beat until fully combined and smooth, forming a cohesive dough.

Portion large balls of dough, about 6 ounces or ¾ cup each. Place 4 balls of dough on each prepared tray and place in freezer. Let chill for 90 minutes.

When ready to bake, preheat oven to 375°F. Place one empty baking sheet upside-down in oven and place one tray of frozen dough on top. Bake one sheet of cookies at a time, until edges and spots on top are golden, but insides are still slightly doughy, about 26 minutes.