Add 1 egg, 110g of butter at room temperature, 3/4 cup of brown sugar, and 1 teaspoon of baking powder and mix well for about 2 minutes. Stir with a whisk until it turns slightly beige.

Add the sifted flour and mix as if cutting with a spatula. If you stir it, the cookies will harden. Add chopped walnuts, chocolate and squid ink and mix. The squid ink is a little salty, so you don't have to add salt to the cookie dough.

If you put the squid ink in from the beginning, the squid ink will unravel and become a gray cookie, but if you mix it at the end, it becomes a Marvel cookie.

Put the dough in a plastic bag into a long cylinder like kimbap and put it in the freezer for about 30 minutes to rest.

After 30 minutes, take out the dough, cut it into appropriate thicknesses with a knife, and bake it in a 180-degree oven for about 15 minutes.