Place the butter and salt in a pot over medium heat. Add the Jerusalem artichokes, potatoes and onions and sweat for 10–15 minutes by placing the lid back on the pot, stirring every few minutes. If the vegetables begin to brown, lower the heat. Add the chicken stock and cook until the vegetables are tender. Purée the mixture and return to the heat. Adjust the seasoning.
To serve: Divide the bacon, chives and goat cheese among 4 bowls. Pour the soup over the top and garnish with the microgreens.