Break the dark and milk chocolate into pieces in a bowl. Bring cream to the boil in a saucepan and pour it over the chocolate. Stir until chocolate has melted, then put bowl over a larger bowl of iced water, to cool. In another bowl, mix marshmallows with the cake and chocolate freckles.
Spray each egg half-mould half with canola oil and line with plastic wrap, leaving a 1cm overhang. Flatten out any air pockets under the plastic wrap. When chocolate and cream mixture has cooled to about 30-34°C (just below body temperature and still runny), combine it with the marshmallow mixture. Fill each half-mould with mixture to just above the rim. Align the 2 halves and gently press together. Wrap whole egg moulds in plastic wrap and refrigerate for 30 minutes.
When set, remove the eggs from moulds. Roll in hundreds and thousands.