Heat the oven to 425°F.

Cut enough parsnip into a small dice to measure 1 cup; cut the remaining parsnips into roughly 1-inch pieces. Cut the apples into chunks.

Arrange the diced parsnips on a prepared baking sheet, toss with ½ tablespoon oil and season with salt. Roast for 10 to 12 minutes, or until golden and caramelized around the edges and easily pierced with a fork. Set aside for serving.

Meanwhile, heat the remaining 1 tablespoon of oil in a large stockpot over medium heat. Add the onion and celery with a pinch of salt and cook until softened and the onion is translucent, about 5 minutes. Add the garlic and cook for 1 minute, until fragrant.

Add the remaining parsnips, apples, mace, thyme bundle and bay leaves. Season generously with salt and add enough stock to just cover the vegetables. It’s fine to hold some back and adjust later. Bring to a simmer, then cover, reduce the heat and cook for 20 to 25 minutes, until the parsnips are very tender and offer no resistance when pierced with a fork.

Remove and discard the thyme bundle and bay leaves. Add the lemon juice, then purée with an immersion blender until completely smooth, or carefully transfer the soup in batches to a countertop blender. Add additional stock as needed and season to taste with salt.

To serve, ladle the soup into bowls and top with a spoonful of apple butter, the roasted parsnips, fresh thyme leaves and, if desired, a sprinkle of truffle salt.