Bring a large pot of water to a boil and add the parsnips. Cook until the parsnips are tender, about 10 minutes. Drain.
Heat a pot over medium-high heat and add the butter and sugar. Allow to melt together. Add onions and saute until caramelized, 6 minutes.
Add parsnips to pot. Turn heat off and add the mascarpone. Stir together and mash, adding parsley, salt and pepper.