Preheat oven to 350℉. Grease the pan. For easy removal of the cookie bars, place parchment paper on the bottom and 2 sides of the pan. Gently grease the other two sides and then set aside. Melt the butter and allow it to cool as you prep the rest of your ingredients.
1/2 cup butter
In a medium sized bowl, add in flour, oats, cinnamon, baking soda, baking powder, and salt. Stir to combine and set aside.
1 3/4 cups rolled oats, 1 1/2 cups all-purpose flour, 1 tsp baking powder, 1/2 tsp baking soda, 3/4 tsp cinnamon, 1/4 tsp salt
In a large bowl, whisk butter and brown sugar. Then whisk in eggs, one at a time, and the vanilla extract.
1/2 cup butter, 1 cup dark brown sugar, 2 eggs, 1 tbsp vanilla
Toss in the dry ingredients. Mix until no dry streaks appear. Don't over-mix. As soon as the flour disappears, stop mixing.
Add in Christmas M&M's and mix in a few more times.
1 cup Christmas M&Ms
Place the batter into the prepared pan and spread evenly. Add some extra M&M's if desired. Bake for 25-30 minutes or until the top is a light golden brown and a toothpick inserted comes out clean. Mine took 28 minutes exactly.
Let the bars cool down completely, slice, and enjoy!