Potato and Celery Root Gratin
By: 
Dish Type: Side Dish
Cuisine: Vegetarian
Ingredient prep: 
Cook time: 
Total time: 
Makes: 4 to 6 servings
 
Don't worry, the truffle salt is optional, but it doesn't cost anywhere near as much as its mushroom source. If you do make the investment, you'll find yourself throwing a pinch on almost everything you cook.
Ingredients
  • 1 clove garlic, halved crosswise
  • 1 t butter
  • 1 large celery root (1 lb.)
  • 2 medium yellow potatoes (1 lb.)
  • 3 to 4 oz. Gruyere cheese
  • ½ C heavy cream
  • 2 t dijon mustard
  • 1 t salt
  • ¼ t pepper (plus more for serving)
Make It
  1. Rub cut side of garlic all over the inside of a shallow, 2 quart baking dish, then grease with the butter. Preheat oven to 375 degrees (F).
  2. Place garlic and 3 cups water in a 3 quart or larger saucepan or pot. Peel celery root (with a knife, not a vegetable peeler) and add peel to the water. Place steamer basket in pot and heat to a boil. While water heats, quarter celery root lengthwise and slice thick, about ¼". Add sliced root to steamer basket, cover pot, and steam 5 minutes. While root steams, peel potatoes and slice thin (1/8" or less). Remove steamed celery root to a large bowl, add potato slices to steamer basket, and steam 3 to 4 minutes, until tender but not fully cooked. Remove to bowl with celery root, separating big groups of slices.
  3. Strain ¾ cup of water from pot through mesh strainer into a 2 cup liquid measuring cup (or medium bowl). Let cool while you grate the Gruyere--you should have about a cup grated. To the water, add cream and dijon and whisk to combine. Season with salt and pepper (you can always add more pepper when serving). Pour over root vegetables and toss gently to combine (tongs work well for this).
  4. Pour root veg mixture into prepared dish, sprinkle with a bit more pepper, and top with grated cheese. Bake about 30 minutes on middle rack, until bubbly. To brown top, broil for a minute or two. Sprinkle with truffle salt before serving, having extra truffle salt available at the table (but warning first-timers, like myself, of its richness).
Notes
Nutrition notes: As written, gluten-free and vegetarian, if vegetarian cheese is used. This is also a particularly decadent gluten-free potato gratin.

Steamer baskets are inexpensive and can often be found in the cookware or produce section at the grocery store. Call me an amateur, but I purchased one for this dish and am sure it will get lots of future use.

This video taught me the best way to peel celery root.
Recipe by Natural Comfort Kitchen at http://www.naturalcomfortkitchen.com/potato-and-celery-root-gratin/