She'd scoff at me for saying this and I do love my grandmother, but boy does she over cook a hardboiled egg :) You know when there's a green ring around the outside of the yolk it's overdone.
I've found my perfect egg. It's somewhere between a soft and hard boiled egg. Every variable is important for consistent results. And once you've found your, you can have it the same every time! You'll have to test it a few times regulating temperatures (egg, water, etc.), time, and egg size. This is what I do:
1. I use an egg right from the refrigerator, set it on the counter for a few minutes while . . .
2. I boil a small pot of water.
3. Boil the egg in the water for exactly 7 minutes.
4. Remove the egg from water and let is sit for 1 minute.
5. Put the egg into a bowl of ice water to cool for a minute.
The whites should be intact, the outside of the yolks just cooked, and the inside of the yolk should be just soft not quite runny. Finish with sea salt & fresh ground pepper.
Reduce time for a runnier yolk, more time for less.