Add butter to a microwave dish and microwave in 20 second increments until butter is fully melted.
Add the brown sugar and white sugar to a large mixing bowl with the melted butter and stir well to combine.
Beat in the vanilla and egg until just combined.
Pour in the flour, baking soda, and salt and mix until just combined.
Stir in the chocolate chips and candies by hand, reserving a few to press onto the tops of the cookie dough, if desired.
Use a large cookie scoop to scoop out 12 cookies and arrange them evenly on a large ungreased baking sheet.
Bake for 10 minutes exactly. Cookies will still be slightly underdone when you remove them from the oven. Do not overbake.
Let sit on baking sheet for 5 minutes before eating. Allow cookies to cool completely before storing in an air-tight container for up to 5 days.
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Notes
To make larger bakery-sized cookies, portion the dough into 9 large balls and bake for 11 minutes exactly. You can use any variety of m&m's you like. Sprinkles also add a little fun pop of color!