Line a baking sheet with parchment paper and set aside.
In a medium bowl, whisk together the bread flour, baking powder, baking soda, and kosher salt.
Using an electric mixer, beat the unsalted butter on medium speed until it comes together in one cohesive mass, about 1 minute.
Add both brown sugar and granulated sugar, and continue to beat for another 1 to 2 minutes, until fully incorporated.
Gradually add the eggs and vanilla and continue beating on medium speed until combined, scraping the sides of the bowl.
Reduce the speed to medium-low and gradually add the flour mixture until just a little bit of flour still remains.
Stir in the dark chocolate chips and walnuts with a rubber spatula.
Divide the dough into 12 even pieces, roughly shaping them into balls.
Place the dough balls on the prepared baking sheet and refrigerate for 30 minutes.
Preheat the oven to 375 degrees F.
Bake for 18 to 24 minutes, or until light golden brown on top.
Let cool for 5 minutes on the cookie sheet before transferring to a wire rack.
Store leftovers in an airtight container at room temperature for up to 4 days.