Mix and melt butter and marshmallows together. Either 2 - 3 minutes in the microwave or several minutes at low to medium heat on the stove.
Stir in Cadbury mini eggs. Make sure they are totally mixed in. Be gentle so eggs don't break too much.
Stir in Rice Krispies cereal. Make sure mixture is evenly distributed.
Spread mixture into greased pan.
Cool for 20-30 minutes and then serve.