Fill a large skillet halfway with water; add a pinch of salt, cover and bring to a boil. Add the pearl onions and cook 1 minute to loosen the skins, then drain and rinse under cold water. Using kitchen shears, trim the root ends of the onions, then peel off the skins. Return the onions to the skillet.
Add the parsnips, ginger, rosemary, garlic, wine, sugar, 1/2 teaspoon salt and 1 cup water to the skillet with the onions. Bring to a boil over high heat and cook, stirring occasionally, until the liquid evaporates and the vegetables are tender, 15 to 20 minutes. (If the liquid evaporates too quickly, add more water, 1/4 cup at a time.) Discard the ginger, garlic and rosemary. (The vegetables can be made up to 3 hours ahead to this point; cover and refrigerate.)
Reduce the heat to medium high; add the vinegar, brandy and butter and cook, stirring, until the vegetables just start to brown, 1 to 2 minutes. Add 2 tablespoons water and cook, swirling the pan, until the vegetables are glazed, about 1 more minute. Season with salt and pepper and top with parsley.