Preheat the oven to 325°F (163°C). Line two light-colored baking sheets with parchment and set aside.

In a large bowl or stand mixer, cream the softened butter with the brown and granulated sugars for 3–4 minutes until lighter in color and fluffy.

Add the eggs and vanilla. Mix until smooth and fully combined, scraping the bowl as needed.

In a separate bowl, whisk together the flour, baking soda, baking powder, and salt (add cinnamon here if using).

Gradually add the dry ingredients to the wet mixture on medium speed until just combined. Avoid overmixing.

Stir in the rolled oats by hand and fold in any mix-ins like chocolate chips or chopped nuts.

Use a medium cookie scoop to portion dough onto the lined baking sheet, leaving about 2 inches between each ball. Flatten slightly if you want a wider cookie.

Bake for 9–12 minutes, until edges are golden brown and centers are set but still soft. Rotate pans halfway if your oven has hot spots.

Let cookies cool on the hot baking sheet for 5 minutes, then transfer to a wire rack to cool completely.