1. Peel and wash the potatoes and cut them into pieces.
2. Fill a pot with water, add salt, and place the potatoes in the cold water.
3. Bring to a boil and cook until tender.
Typically, cooking takes 20 to 25 minutes from the cold start.
4. Drain the potatoes and let them dry for a moment.
5. Add the butter in small pieces and mash the potatoes with a potato masher or fork.
6. Add warm milk, from 10 cl to 30 cl, to achieve the desired consistency.
7. Season with salt, pepper, and a little nutmeg.
8. Add the egg if you have chosen this option and mix again.
9. Adjust the seasoning of your grandma's mashed potatoes by adding more salt and pepper if needed.