Preheat the oven to 350 degrees.
In a large bowl combine the butter, sugar, and brown sugar. Mix well to combine.
Add in the egg and vanilla and mix well.
In a medium bowl combine the flour, baking soda, baking powder, and salt. Mix and then add to the butter mixture. Mix until combined.
Gently fold in 1 cup of the white chocolate chips.
Spread into a 9 x 13 pan sprayed with cooking spray and then bake for 15 minutes.
Remove from the oven and sprinkle with marshmallows and M&M's. Place back in the oven for 3-4 minutes or until marshmallows just start to brown.
Quickly sprinkle with remaining white chocolate chips and sprinkles.
Cool completely on a wire rack.