Cut the unpeeled potatoes into chunks and place in large pot of cold water with 1 T of salt. Bring to a boil and then lower the heat to maintain a steady simmer. Cook about 22 minutes, until potatoes are very tender but not falling apart.
As soon as potatoes are on the stove, heat the olive oil in a large sauté pan over medium-high heat. When hot, cook the sausage links until nicely browned and internal temperature is at least 165F. When cooked, remove sausages from pan.
Lower heat to medium and add leeks to pan used to cook sausage. Cook leeks about 5 minutes until softened and starting to pick up some color. Add the chard to the pan along with the salt and pepper. Cook until the greens have wilted and given up all of their liquid. Turn off the heat.
By now the potatoes should be done. As soon as they are, add the potato chunks to the pan along with the stick of butter cut into large pieces. Mash the potatoes being sure to distribute the butter and vegetables in the process. Taste for seasoning and serve with sausages.