Preheat the oven to 150*C. Bring a small pan of water (a few inches high) to the boil, and then turn down to a very bare simmer. Rub the inside of a large bowl, or the bowl of your stand mixer, with the lemon juice, using the cut side of the lemon. Add the egg white, sugar and salt. Place the bowl over the small pan of water, and stir constantly for 8-10 minutes until the mixture is warm to the touch and you can feel no grains of sugar. At this point, either whip on high speed on your stand mixer for 4-6 minutes until smooth, stiff and glossy or use electric hand beaters.
Add the meringue to a piping bag.
Line a baking trays with baking parchment, using a tiny bit of the meringue underneath each corner to hold the paper in place. Cut a tiny hole at the end of the piping bag and pipe small dots in varying sizes (the size of a lentil, pea, grape etc). Once you have piped around 40 circles, lay another piece of baking parchment on top of the piping and gently press down - this will help you get the perfect eye shape. Leave the baking parchment on top while you bake.
Place tray in oven, and turn off the heat. After 30 minutes remove the eyes. Peel back the baking parchment and leave to cool.
Melt the chocolate over a double boiler or in the microwave in 30 second bursts, stirring regularly. Pipe small chocolate dots in the centre of the eyes and set aside.
Mix your green dye into buttercream and pipe onto 12 shop bought fairy cakes. And dot lots of eyes over each green monster.