Place the potatoes in a saucepan and cover with enough water to cover the potatoes by one inch.
Bring to a boil over medium-high heat. Then lower the heat to simmer for about 20 to 25 minutes. Potatoes are done when they can be easily pierced with a fork.
While the potatoes are boiling, heat the milk, butter, herbs, and optional onion in a small saucepan over low heat.
Remove the herbs and onion (if used) from the milk.
When the potatoes can be easily pierced with a fork, drain the water and run the potatoes through a potato ricer or food mill.
Add the warm milk to the processed potatoes, and season with salt and pepper to taste. Stir to combine.
Serve immediately. The potatoes may become gummy if allowed to cool too much.