Place the chocolate in a heatproof bowl and sit the bowl over a saucepan of gently simmering water, stirring occasionally, until melted. Once melted, remove from the heat and stir in the finely crushed cornflakes, stirring well until you have an even mixture.
Grease the insides of egg poaching cups with oil and line with clingfilm. Press the mixture into the base of the cups, leaving a hole in the centre; this will form the nest part. Chill the cups until the nests are set. Turn out from the moulds once set and fill the middles with the mini eggs before serving.