Preheat your oven to 350°F (175°C) to ensure even baking.
Line a baking sheet with parchment paper to prevent sticking and ease cleanup.
In a large mixing bowl, cream together the softened butter, light brown sugar, and granulated sugar with an electric mixer until smooth and fluffy, about 2-3 minutes. Beat in the egg and vanilla extract until well combined.
In another bowl, whisk together the all-purpose flour, instant vanilla pudding mix, baking soda, and salt until evenly mixed.
Gradually add the dry ingredients to the wet mixture, mixing until just combined. Avoid overmixing to maintain softness.
Gently fold in the M&MS and semi-sweet chocolate chips until evenly distributed throughout the dough.
Using a cookie scoop or tablespoon, scoop mounds of dough onto the prepared baking sheet, leaving space for spreading.
Press a few extra M&MS and chocolate chips into the tops of each cookie mound for a bakery-style look.
Bake in the preheated oven for 10-12 minutes until edges are lightly golden; centers may look slightly underbaked.
Remove from oven and cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. Enjoy!