Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper.
Add the 1 cup butter, 1 1/4 cup light brown sugar, and 1/2 cup granulated sugar to a large mixing bowl. With a hand mixer on medium, beat until creamed.
Add in the 2 large eggs and 2 teaspoons vanilla extract and beat until combined.
Add in the 3 1/4 cups all-purpose flour, 1 teaspoon baking soda, and 1/2 teaspoon salt. Beat until the flour is almost completely incorporated.
Add in the regular 1 1/2 cups M&M candies, 1/2 cup mini M&M candies, and 1 cup milk chocolate chips. Mix until the candies and chips are evenly distributed.
Using a 1 1/2 tablespoon cookie scoop, scoop the cookie dough onto the prepared baking sheet.
If you have additional candies and chocolate chips, add 3 to 5 of a combination of the two to the top of the cookie dough.
Place in the preheated oven and bake for 12 to 14 minutes until the edges are golden brown.
Let the cookies cool on the baking sheet for 5 to 10 minutes before transferring to a wire rack or a paper towel to cool completely.
Place in an airtight container and store at room temperature for up to 5 days.
Notes
Storage: Store in an airtight container at room temperature for up to 5 days.