Make a small horizontal slice along the largest end of the egg, enabling it to stand by itself but still contain the yolk inside. Carefully slice off the top of the egg in a 'shell-like' pattern, about 2/3 of the way from the bottom.
Scoop out the yolk and place in a bowl with your mayo, mustard, salt and pepper and beat with a fork until smooth. Be careful as the egg white will be fragile.
Place the mixture into a pipping bag and squeeze into the base of one your egg white bases. You can also just use a spoon (like I did), just looks a little more 'rugged' shall we say. Place two peppercorns for the eyes and cut a tiny chunk of carrot/red pepper for the nose. Place other half of egg white (the hat) on top.
Garnish as you wish! I made a base out of toast strips to keep the egg secure (photo beside) and surrounded with fresh garden salad and chilli flakes.