Preheat the oven to 300 degrees F (150 degrees C).
Whisk flour, baking powder, and salt together in a bowl.
Beat butter and sugar with an electric mixer in a medium bowl until fluffy, 2 to 3 minutes. Stir in flour mixture in two batches, then stir in chocolate chips and walnuts.
Roll or scoop dough into walnut-sized balls and place 1 1/2 inches apart on ungreased cookie sheets. Press on each cookie slightly to flatten.
Bake in the preheated oven until light golden brown, 15 to 20 minutes.
Remove from the oven and transfer to wire racks to cool.