In a large saucepan, melt the butter and the marshmallows on a low heat.
Once a fluffy paste forms, take off the heat and stir in the rice crispies.
Place the mixture into a greased tin (I used a medium-sized roasting tin!). I used baking paper but I'd advise against it as they got stuck to it... Flatten the mixture.
Melt the milk chocolate (I used a microwave) then drizzle this over the crispy cake.
Crush mini eggs and scatter these across the top.
Leave to set in the fridge, then cut into 15-18 squares.