1) Lightly soften the butter with a hand mixer at room temperature (microwave for 15s - 30s to room temperature ~ 20 celcius)
2) Add granulated sugar, brown sugar and salt and whisk for about 1 minute at medium speed with a hand mixer.
(In the original recipe, it is said to be 2 minutes at medium speed, but it is enough to whip for 1 minute. Be careful that over whipping spreads the cookie and looks ugly)

3) Add egg, vanilla extract, and lemon juice at room temperature and whisk for 1 minute at medium speed.
(The original recipe says 2 minutes, but 1 minute is enough. Do not overmix)

4) Sift flour, baking soda, and cinnamon powder and fold with a spatula.
5) When there is some powder remaining, add chocolate chips, walnuts, and oatmeal and mix evenly.
(The walnuts were pretreated and used: boiled in boiling water and then baked for 2 hours at 100 degrees Celsius to completely remove moisture)

6) Pan with a 50mm diameter scoop. If you don't have a scoop, divide it into rounds of 50g each.
(The scoop size is slightly smaller than the original recipe)

7) Press the top slightly to flatten it, and bake it in a preheated oven at 150 degrees Celsius (300 degrees Fahrenheit) for 16 minutes. (Unox convection oven)
* The original recipe says 150 degrees Celsius 20 to 23 minutes, but in my oven, 16 minutes was just right. Adjust the time by looking at the color and condition of the cookie. When overbaking, be careful that the cookie will become hard.

(150 c for 16 mins when fresh bake, for 20 mins if bake from fridge)

Storage: Cookies can be individually packaged after cooling, and stored for 5 days at room temperature and frozen for more than 1 month.

Make a head of time:
The remaining cookie dough is scooped into a cookie scoop and frozen in the shape of a ball. (For 2-3 months).
When you bake it, you can bake it without thawing. Then increase the baking time by 1-2 minutes.