In the bowl of an electric mixer, beat butter, powdered sugar and vanilla until light and fluffy.
Add egg and whisk until combined.
Using the paddle attachment, turn the mixer on low and slowly add the flour, pudding mix and baking soda. Mix until combined. Add white chocolate morsels and stir until combined.
Refrigerate dough and heat oven to 375 degrees F.
Line a baking sheet with parchment paper.
Use a medium sized cookie scoop to scoop out the dough into balls and space 2 inches apart on the baking sheet.
Press the M&Ms candies randomly on top of the cookie dough balls.
Bake 10-12 minutes, just until golden brown on the edges.
Cool for 1 minute on the pan then transfer to a wire rack to cool for 30 minutes.