Making Christmas Monster Cookies is a straightforward and enjoyable process. Follow these steps to create your festive treats:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper.
2. Cream Butter and Sugars: In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
3. Add Eggs and Vanilla: Beat in the eggs one at a time, followed by the vanilla extract, mixing until well combined.
4. Mix Dry Ingredients: In a separate bowl, whisk together the flour, baking soda, and salt.
5. Combine Mixtures: Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Do not overmix.
6. Fold in Add-ins: Gently fold in the chocolate chips, M&Ms, nuts, and oats (if using), ensuring an even distribution throughout the dough.
7. Scoop Cookies: Using a cookie scoop or tablespoon, drop rounded balls of dough onto the prepared baking sheets, spacing them about 2 inches apart.
8. Bake: Place the baking sheets in the preheated oven and bake for 12-15 minutes or until the edges are lightly golden, and the centers are set.
9. Cool: Remove from the oven and let the cookies cool on the baking sheets for 5 minutes. Then, transfer them to wire racks to cool completely.

These simple steps will guide you in creating delicious Christmas Monster Cookies that are sure to impress!