Fill a pot with a couple inches of water and steam potatoes for about 15 minutes or until they are cooked and you can easily slide a fork through one. If you don't have a steamer basket, boil in water.
While potatoes are cooking, thinly slice the onion, then combine all remaining ingredients in a bowl and whisk until smooth.
When potatoes are ready, drain the hot water and replace with cold water. Using your hands, peel the potatoes. The skin should slide off easily.
Add potatoes and onion to the dressing and mix. As you mix, the potatoes might break apart a little - this is good! It will help them not be big, giant bites.
Enjoy immeditely while warm or serve cold from the fridge.
Store about 4-5 days in the fridge.