Line a baking sheet with parchment paper.
To prepare the dry ingredients, in a large bowl, combine the all-purpose flour, oat flour, baking soda, salt, and cinnamon. Set it aside.
To prepare the wet ingredients, in a separate bowl, add the softened butter, cane sugar and coconut sugar. Using a hand mixer at medium speed, cream for approximately 5-6 minutes.
Add the vanilla extract and lemon juice and mix for 30 seconds.
Add the eggs into the creamed mixture and mix until smooth, approximately 2 minutes.
Add the dry mixture to the wet mixture in 3 batches while running the mixer at a low speed. Before adding each batch, scrape down the sides of the bowl with a spatula, making sure all the ingredients are incorporated.
Fold in the chocolate chips and walnuts. Mix until combined and well distributed.
Scoop the dough with a large (3 tablespoon) ice cream scoop and place each cookie on the prepared baking sheet. You should have about 20 cookies each weighing approximately 68 gr.
Cover the baking sheet loosely with plastic wrap, place it in the fridge and let it rest overnight.
When you are ready to bake, preheat the oven to 300 degrees F. There is no need to bring the cookies to room temperature. You can make them right out of the fridge.
Line another baking sheet with parchment paper. Divide the cookies using two baking sheets, making sure that they are 2 inches apart from one another.
Bake, rotating halfway through, for 20-23 minutes until they are lightly browned.
Remove from the oven and let the cookies sit on the baking sheet for 5 minutes. Then, transfer to a wire rack and let cool.