Celery Root Puree with Crispy Arugula

Puree:

2 pounds (about 2) celery root, peeled and cut into 1-inch chunks

1 1/2 pounds (about 2) russet potatoes, peeled and cut into 1-inch chunks

1 small yellow onion, peeled and cut into quarters

2 cups whole milk

2 cups water

5 tablespoons butter, cut into pieces

Salt and white pepper

Arugula: 

3 cups arugula

3 tablespoons olive oil

Salt and pepper

Heat oven to 400F. Line a baking sheet with parchment. Combine celery root, potatoes and onion in a Dutch oven or soup pot. Add milk and water and season with salt. Bring to a boil then reduce heat and simmer until soft, about 20 minutes. 

Meanwhile, prepare arugula: In a mixing bowl, toss arugula and olive oil. Spread out on prepared baking sheet and season with salt and pepper. Bake until wilted and slightly crisp, about 12 minutes. 

Drain boiled vegetables, reserving cooking liquid. Working in batches, puree cooked vegetables with butter and about 1/2 cup cooking liquid until smooth. Season with salt and white pepper. Serve puree topped with arugula.