Here is an unusual spin on mashed potatoes. Browning the vegetables and cooking them in minimal liquid before mashing heightens their flavor. You can use water, but this dish is even better when made with vegetable stock.
1. Heat 2 Tbs. oil in large skillet over medium heat. Add celery root and potatoes, sprinkle with salt and pepper, and cook, stirring often, until mixture begins to brown, 5 to 7 minutes. Add stock, stirring to scrape up any browned bits.
2. Cover, and cook until vegetables are tender, 10 to 12 minutes. Mash vegetables, stirring to soak up pan juices. Stir in lemon juice and remaining 1 Tbs. oil. Taste, and add more salt, pepper and lemon juice if desired. Serve warm.