Preheat your oven to 350 degrees Fahrenheit. This step is essential for achieving that perfect cookie texture. While the oven warms up, line two large baking sheets with parchment paper.
In a medium bowl, combine the all-purpose flour, baking soda, ground cinnamon, salt, and old-fashioned oats. Whisk them together until well mixed, and set the bowl aside for later.
In a large saucepan, melt the butter over medium heat. Stir it frequently with a wooden spoon. Continue cooking until the butter smells nutty and turns a light golden brown, with tiny golden specks at the bottom.
Once browned, remove the saucepan from heat. Carefully scrape the browned butter into a large mixing bowl.
In the bowl with the browned butter, whisk in both the light brown sugar and granulated sugar along with the vanilla extract. Beat well for about two minutes until everything is combined and creamy.
Add in the large eggs and large egg yolk, whisking until they are fully incorporated into the batter.
Now it’s time to fold in the dry ingredients. Gently combine the flour mixture with the batter, being careful not to overmix.
Using a large spring-loaded scoop or spoon, scoop about three tablespoons of cookie dough into the palm of your hands and roll it into a ball. Place the dough balls on the prepared baking sheet, leaving about two inches of space between each cookie to allow for spreading.
Bake the cookies one tray at a time for 12 to 13 minutes. You want them to spread out and become lightly golden brown.
As soon as they come out of the oven, press extra M&Ms and pecans on top of the warm cookies for that added festive touch.