1. whisk together flour, cinnamon,baking soda, and salt. Set aside.
2.In a bowl of a stand mixer with paddle attachment, or large mixing bowl using an electric mixer, cream together butter, brown sugar, granulated sugar for one to two minutes until well combined. Add the egg and vanilla extract and mix.
3.Slowly mix in the flour mixture and then the oats, chocolate chips and walnuts making sure to scrape down the sides of the bowl as needed.
4. Cover the cookie dough tightly with plastic wrap and refrigerate for 30 minutes.
5. Preheat oven to 350 F . Line two large baking sheets with parchment paper or silicone baking mats and set aside.
6. once dough is chilled, remove from refrigerator. Using a 1 1/2 to 2 tablespoon cookie scoop drop the dough onto the cooking sheets.Roll the dough into balls and slightly flatten with the palm of your hand. Leave a little room between each because they will spread a little while they bake.
7. Bake in separate batches at 350 F for 10-12 minutes or until the edges are lightly golden brown and the top is set. Remove from oven and cool on the baking sheet for 5 minutes, then transfer to a wire wrack to finish cooling.
Notes: Prep time includes 30 minutes of chilling time. Allowing the dough to cool for 30 minutes will help the cookies to bake up thicker. If you prefer your cookies to be a little thinner , you may skip the chilling of the dough.
