Heat your oven to 350°F and line two baking sheets with parchment paper. Grab a medium mixing bowl and combine 1 cup flour, 1 tsp cinnamon, 1/2 tsp baking soda, and 1/4 tsp salt. Whisk it together for about 30 seconds until everything's evenly mixed. Set this aside — you'll use it in a minute.

In a large bowl, beat 1/2 cup softened butter with 1/2 cup brown sugar until it looks light and fluffy, about 2 minutes. Don't skip this step because it creates air pockets that make the cookies soft instead of dense. Scrape down the sides with a spatula so nothing gets left behind.

Add 2 eggs one at a time, beating well after each one. Then pour in 1 tsp vanilla powder and mix until you can't see any white streaks. This base is your foundation, so make sure it's really combined before moving on.

Sprinkle the dry flour mixture over the wet ingredients and stir just until combined — literally 20-30 seconds. I accidentally overmix sometimes and the cookies turn out tougher, so be gentle here. Fold in 1 cup rolled oats and 1/2 cup chopped walnuts until everything's evenly distributed.

Drop rounded tablespoon-sized portions onto your lined baking sheets about 2 inches apart. These oatmeal cookies recipe batches will spread a little, so don't crowd them. You should get about 24 cookies total from one batch.

Bake for 12 minutes until the edges look set but the centers still look slightly underbaked. This is the secret to chewy cookies — they'll continue cooking on the hot pan after you pull them out. If you bake them until they look completely done, they'll harden as they cool.

Let the cookies sit on the baking sheet for 5 minutes, then transfer them to a cooling rack. They'll firm up as they cool, and by the time they're room temperature they'll have that perfect texture. Store them in an airtight container for up to five days.