Melt the chocolate in the microwave. Fill each egg mould with about 1 teaspoon of chocolate. Let set for a few minutes. Add another layer of chocolate on the edge of the egg and put in the freezer to set. Put the rest of the chocolate in a piping bag.
Cream butter with an electric mixer until pale and fluffy. Add condensed milk, vanilla and salt and mix until combined. Add icing sugar gradually and 30ml milk and mix. Set aside about ¼ of the mix in a small cup and add yellow food colouring. Spoon in a piping bag. Add the other 30ml milk in the main mixture and mix well. Spoon in a piping bag.
Take the half eggs off their mould. Fill each half egg with the white mixture then add a bit of yellow mixture in the middle. With the piping bag of melted chocolate, draw a line of melted chocolate over the edge of one side of the egg, then stick with the other side. Let dry and refrigerate to set.