Clean and trim the roots off the ramps. Cut the in half, separating the bulb from the green leaves, and set the leaves aside for later.
Finely chop the bulbs and the sweet onion and add to a medium/large pot with some olive oil and sweat them down (careful not to get color on them) over a low/moderate heat
As the ramp bulbs and sweet onion cook down, peel and cut the potatoes into small cubes (the size doesn’t really matter--just think: the smaller they are the quicker they cook) and add those to the pot.
Cover the potatoes with stock and bring to a boil. Then reduce the heat and cover (so the liquid doesn’t evaporate, but the potatoes cook until tender.)
Roughly chop the ramp leaves and once the potatoes are just about fork tender add the leaves into the pot and stir well and allow to wilt for a few minutes. At this point taste and adjust the salt.
Blend (an immersion blender works well) until smooth. Taste and adjust the seasoning and serve with a dollop of creme fraiche. Or optionally, stir in some heavy cream before serving