1. Heat 2 tablespoons oil and garlic in a large Dutch oven over medium-low heat until garlic is golden and fragrant, 7 to 9 minutes. Add parsnips, celeriac, potatoes, broth, water, thyme, and 1 tablespoon salt and bring to a boil over high heat. Reduce heat to medium-low, cover, and simmer until vegetables are fork-tender, 20 to 30 minutes.
2. Place colander over a large bowl and drain vegetables, reserving cooking liquid; discard thyme.
3. Working in batches, spoon vegetables into a ricer, then press back into now-empty Dutch oven. Stir 1/2 cup reserved cooking liquid and remaining 1 tablespoon oil into vegetables until smooth, adding additional cooking liquid for consistency if needed; season with salt and pepper to taste.
4. To serve, transfer mash to a bowl, drizzle with extra oil, and sprinkle with chives.
Source: Hannaford fresh Magazine, November - December 2016