Melt the butter, sherry wine vinegar and sugar in a small pan over medium heat. Stir well to combine and remove from the heat.
Quarter the parsnips and cut the carrots into 2-inch pieces. Put on a baking sheet and drizzle with the butter and sherry mixture. Season with salt and pepper, (lots of pepper) and toss to thoroughly coat all the vegetables. Bake in the preheated oven until the vegetables are golden brown. About 5 minutes before the vegetables are done remove them from the oven, sprinkle with fresh thyme and mix to combine. Return to the oven and bake until cooked through about 5 more minutes. Serve.