Preheat oven to 350 degrees and line a large baking sheet with parchment paper.
Place butter, brown sugar and granulated sugar in a stand mixer or large bowl with a hand mixer. Beat to combine then add egg and vanilla beating to combine.
Add your flour, pudding mix, baking soda, corn starch, salt and 1 cup of dark chocolate chips and 1 cup of Christmas themed m&m's. Fold the cookie dough until combined.
Using a cookie scoop or your ¼ cup dry measuring cup, scoop out the cookie dough and place the cookies on a parchment lined baking sheet.
Place the cookies in the refrigerator to chill for 15 minutes.
Make sure the cookies are 2 inches apart on a parchment lines baking sheet.
Bake the cookies for 15 minutes at 350 degrees.
Remove the cookies from the oven and allow to cool