whole eggs in shell
onion shells - just the papery parts, not the fleshy parts
oil (I use olive)
over safe pan with tight lid or crockpot
Place a layer of onion skins on the bottom of the pan. Then add a layer of whole raw eggs. Place onion skins between eggs and on top of eggs. If desired, repeat layers.
Add water to cover at least an inch over. Drizzle olive oil over the water to make a thin slick (important!). Lid pot.
Cook at 225 or on low in a crockpot for at least 8 hours. Longer is better. I have cooked them for as long as 16 hours and they were delicious. Plunge eggs into cold water after cooking for peel-ability.
Eggs inside will be a different color, flavor and consistency than you are used to in a hard cooked egg (I don't make plain hard cooked eggs anymore if I can use this method). Use them any way you would use a hard cooked egg - plain with a little salt and pepper, egg salad, etc.
To be extra fancy, a variation on this recipe is to color the shells of the eggs with white crayon, or to tie flowers/leaves to the eggs with string, or use tied up pantyhose to keep them next to the shell. This "blocks" the dying effect and makes a pattern or image on the shell.