Preheat oven to 350°F.
Mix together melted butter and the entire contents of the Jello packet.
Add the egg and cake mix.
Pat into a foil lined and well greased 9×13″ pan.
Sprinkle white chocolate chips over the cake mix crust.
Pour bag of M&Ms over the white chocolate chips.
Drizzle sweetened condensed milk over everything.
Bake at 350°F for 25-30 minutes.
Allow bars to cool before cutting.