Line an 8 x 8 inch tin with parchment paper, set aside.
In a large bowl, add the butter and the marshmallows. Melt together in the microwave for 2 - 3 minutes, until the butter is melted and the marshmallows have puffed up.
Working quickly, add the funfetti cake mix and the ramen noodle to the marshmallow mixture, breaking the ramen on to tiny pieces as you go. Fold together until all of the ramen is coated the cake mix has been absorbed
Transfer the mixture to the prepared tin and sprinkle over the rainbow sprinkles. Allow to set at room temperature for a minimum of 3 hours - overnight.
When ready to serve, slice into 9 large squares and enjoy.