In the bowl of a stand mixer fitted with the paddle attachment, beat 1 1/2 cups butter, 1 1/2 cups packed dark brown sugar, and 3/4 cup granulated sugar on medium speed until combined and smooth.
Add 3 large room-temperature eggs and 2 teaspoons vanilla extract; beat until just combined and no large streaks of egg remain.
Add 1 1/4 cups cake flour, 1 1/2 cups all-purpose flour, 2 teaspoons baking powder, 1 1/2 teaspoons baking soda, and 1 teaspoon salt; mix on low speed until the dough is just barely combined.
Remove the bowl from the mixer and fold in 3 cups semi-sweet chocolate chips and 1 1/2 cups walnut pieces by hand until evenly distributed.
Cover the bowl with plastic wrap and chill the dough in the refrigerator for 30 to 60 minutes.
Preheat the oven to 400°F (200°C) and line baking sheets with parchment paper or silicone mats.
Portion the chilled dough into twelve 6-ounce portions (use a scale). Shape each portion into a rough, rustic blob—do not smooth into a tight ball.
Bake the cookies for 10–11 minutes, until the tops and bottoms begin to turn golden brown.
Remove the baking sheet from the oven and let the cookies cool on the pan for 12–15 minutes to finish cooking and set.
Serve the cookies the same day for best texture.