I've been making deviled eggs for years but I've never shared my recipe here. It's fairly simple but very, very delicious. I don't measure the mayo or mustard, just go by feel and taste.
I've never been good at piping the filling back into the eggs, so excuse the unstyled photos. We inhaled these at Easter. Baby Girl loves them - she had three. Next year I'm making a full dozen since there were no leftovers.
Put the eggs carefully in a large pot. Fill the pot with cold water so the eggs are completely covered. Put the pot on the stove and bring to a boil. Turn the heat off, cover the pot and allow to sit for 12 minutes. Drain the eggs and immediately submerge in ice water. Allow to cool completely.
Once the eggs are cool, peel them. Cut each egg in half and remove the yolks to a bowl. Mash each yolk as you add it to the bowl so the yolk is a smooth paste. Add some mayo (start with a few tablespoons) and mash into the yolks. You want the mixture to be smooth and creamy. Add more mayo as needed to get the consistency you want. Add a few squirts of mustard to taste. The more mustard you add the spicier they'll be. Season with salt and pepper.
Pipe or spoon the filling back into each egg half.