1, Peel the celery root with a vegetable peeler and cut it into cubes. If there are brown areas that do not peel off with the vegetable peeler, cut them off and discard them.
2. Boil the celery root in salted water until soft.
3. Leave the skin on the potatoes and boil in salted water until soft. Let the potatoes cool slightly so they aren’t too hot to the touch. Then peel the skin off. The skin falls off easily when the potatoes are still warm. I find this method of boiling potatoes saves times vs. peeling the potatoes first. Plus, the potatoes absorb less water with the skin on, so they are firmer.
4. Purée the potatoes and parsnips using your favorite method—a potato ricer, food mill, or an immersion blender. You can also mash them using a potato masher. Traditionally this recipe is pureed to a smooth consistency but if you prefer mashed it is still delicious. Lumps or no lumps, that’s up to you.
5. Add cream, milk, butter, sea salt, and pepper to your liking.