Preheat the oven to 350 degrees.
Combine the melted butter, brown sugar & granulated sugar in the mixing bowl. Beat well.
Slowly beat in the egg & vanilla.
Mix in the flour, baking soda & salt on low, working the dough until the ingredients are just combined. The dough will be soft.
Fold in the semi-sweet & white chocolate chips followed by 1/2 of the M&M’s & all of the sprinkles.
Portion the dough into 9 large balls & place on a parchment-lined baking sheet about 2″ apart.
Bake 11 minutes. They will look underdone – but do not overbake.
Press additional M&M's into the tops of the baked cookies before they set.
Let the cookies set on the baking sheet for at least 5 minutes before transferring to a wire rack to finish cooling.