Start by peeling (optional) and chopping potatoes. Add them to a pot with enough water to cover the potatoes plus an inch. Bring to a boil, then reduce the heat to low and cook the potatoes until tender, about 25 minutes.
While potatoes are boiling, chop 1/2 onion and green onions, put aside.
Once potatoes are tender, drain them and rinse with cool water then set aside to cool.
When the potatoes are cool to the touch, add them to a bowl along with the onions, mayo, mustards, and spices. Add the mayo a little bit at a time until you've reached desired creaminess.
Refrigerate for at least 30 minutes prior to serving.
