Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper or silicone baking mats.
In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
In a large bowl, beat the butter, granulated sugar, and brown sugar with an electric mixer on medium speed until light and fluffy, about 2-3 minutes.
Add the vanilla extract and eggs, one at a time, beating well after each addition.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Gently fold in the Christmas M&M's and semi-sweet chocolate chips, if using.
Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart.
Bake in the preheated oven for 10-12 minutes per batch, or until the edges are lightly golden but the centers are still soft.
Allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely. Serve and enjoy!
