Put the eggs in a pan of cold water. Bring to the boil, turn off the heat, cover and rest for 6 minutes. Drain and rinse the eggs and put them in a bowl of very cold water. Rest for 15-20 minutes, then peel the eggs.
Cut the eggs in half, lengthwise. Scoop out the yolks into a mixing bowl. Add the mustard and mayo, then smash with a fork until you get a smooth, slightly textured paste. Add more mayo if it’s not creamy enough. Season to taste, then fill the egg white halves with the mixture.
Now the fun part - decorating the eggs: use capers for the eyes, carrot /radish/red pepper slices for the ears; celery/ olive/radish/pepper pieces for the nose; chives or dill for the whiskers. (You can use other things too: pickle, ketchup, nuts, seeds, pesto etc )
Enjoy!