Preheat the 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.
Mix in the vanilla extract. Add eggs one at a time, beating well after each addition.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Stir in the Christmas M&M’s and chocolate chips.
Drop rounded tablespoons of dough onto the prepared baking sheets, leaving about 2 inches between each cookie. Bake for 10–12 minutes, or until the edges are golden but the centers still look soft.
Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
Serve and enjoy with milk or your favorite holiday drink.