Cream the butter and sugar thoroughly.
Add the egg and mix well.
Add cake flour, bread flour, baking powder, and salt, then mix.
Add chocolate chips and walnuts, and mix evenly.
Shape the dough into thick, round balls.
Let the dough rest in the refrigerator for at least 1 hour.
Bake in a preheated oven at 180°C for 12-15 minutes.