in a large glass microwave safe bowl combine cake mix and powdered sugar. stir to combine.
add milk by sprinkling around on top of mix and arrange butter around on top. no need to mix it in.
microwave on high for about 2 1/4-2 1/2minutes so butter is melting and everything gets hot. (microwave ovens vary, u just want the butter melted and the mix hot enough to melt the chocolate chips)
immedietly remove from microwave and stir quickly but gently until all butter and milk is incorporated.
immedietly while its still warm add white chocolate chips and continue to stir until mostly melted.
add about 1/4 of your sprinkles to the mix. fold in. mix will be thick and getting harder to mix.
by now mix is starting to cool.. transfer mix by spreading it into a 9x7 greased pan.
after spreading mix in pan sprinkle the rest of your sprinkles across your fudge and gently with clean hands press sprinkles down so they stick well and they all won't fall off when u go to eat it.
place in fridge to set. batter should now be firm and cold and fudgy like. about 2 hours.
keep refridgerated until ready to serve.
cut into about 28 - 1" squares.
serving size is one 1" square.
NOTE: MICROWAVE OVEN MAY VARY.. MINE WAS 1200 WATT.. U JUST WANT TO HEAT ON HIGH UNTIL BUTTER IS MOSTLY MELTED. DO NOT OVER HEAT. THANK YOU. :)
note: if too thick and super hard to stir u may need to add a tbl. or 2 of more milk depending on brand of cake mix used. or if u want them to be a softer fudge just add a bit more butter when heating.