Step 1: Preheat your oven to 375°F (190°C). Line two baking sheets with parchment paper or silicone baking mats.
Step 2: In a large bowl, cream together the softened butter, granulated sugar, and light brown sugar with an electric mixer until light and fluffy (about 2-3 minutes).
Step 3: Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Step 4: In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix.
Step 6: Gently fold in 1 cup of the M&M's Christmas Candies. Reserve the remaining 1/2 cup for topping.
Step 7: Drop rounded tablespoons or use a cookie scoop to place dough balls onto the prepared baking sheets, about 2 inches apart. Press a few of the reserved M&M's onto the top of each dough ball for a festive look.
Step 8: Bake for 10-12 minutes, or until the edges are lightly golden and the centers are still slightly soft. Do not overbake for chewy cookies.
Step 9: Remove from the oven and let the cookies cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely. Enjoy your festive M&M Christmas Cookies!