Start by preheating your oven to 350°F and lining your baking sheet with parchment paper.
Whisk together the cake flour, baking powder, and baking soda in a large bowl.
In a separate bowl, mix the room-temperature unsalted butter and brown sugar with a stand or hand mixer. Mix on low speed until the mixture is light and fluffy. Then add egg and mix until well combined.
Gradually sift the dry ingredient mixture into the wet ingredients, mixing until combined. Be careful not to overmix, as this can lead to tough cookies.
Stir in the dark chocolate chips (or semi-sweet chocolate chips) and chopped walnuts. The dough should be filled with delicious chunks and crunchy walnuts.
Cover the mixture with plastic wrap and put it into the refrigerator for 10-15 minutes. (Do not skip this important step!)
Use a cookie scoop or your hands to portion it into equally-sized balls. Roll each portion into a smooth, round ball between the palms of your hands. The size of the balls will decide the size of your cookies. Press down on the top of each dough ball with a fork. Make a crisscross pattern by pressing the fork down once, rotating it 90 degrees, and pressing down again. Repeat for each cookie.
Arrange the shaped cookie dough balls onto parchment-lined or greased cookie sheet, leaving enough space between them to spread during baking.
Bake in the preheated oven for 10 minutes. Take the baking sheet out of the oven, press down a few more nuts and chocolate chips on top of each cookie, and bake for an additional 5 minutes. You can skip this step, but I love my cookies loaded with all the goodies, and they turn out the best! For a chewy texture, do not overbake.
Once out of the oven, transfer the baked cookies to a cooling rack to cool. They'll continue to firm up as they cool down.
Serve with a glass of milk or as is. Enjoy!