Preheat oven to 425°F. Line a rimmed baking sheet with parchment.
Put carrots and parsnips in a large bowl; add oil, butter, maple syrup, thyme, and wine, and season with salt and pepper. Loosely mound vegetables in center of parchment on baking sheet. Fold parchment up over vegetables in the center and at edges, sealing it well so steam won’t escape.
Bake until veggies are crisptender, about 30 minutes. Transfer packet to a platter and carefully cut open (hot steam will escape). Sprinkle additional thyme on top, if desired.