How to make a root vegetable au gratin

• Peel celery root and sweet potatoes. (Leave the skin on the Yukon Gold potatoes.)
  
• Slice off the fuzzy, knobby ends of the celery root.
  
• Slice vegetables in thin uniform slices. A mandolin is best for this task.
  
• Combine your root vegetable slices in a large mixing bowl with 3 large pinches of kosher salt.
  
• Add 1 cup vegetable stock.
  
• Add the leaves from 3 sprigs of fresh thyme.
  
• Toss with your hands to spread thyme and salt evenly throughout the vegetable mixture.
  
• Place in a large gratin dish or flat baking dish.
  
• Pour 2 cups heavy cream over the vegetables.
  
• Bake in a 450 degree oven for 55 minutes or until golden brown and bubbly.
  

Martha's root vegetable recipe calls for:

2 pounds Yukon Gold potatoes

3 large heads celery root

2 pounds sweet potatoes

2 cups heavy cream

1 cup vegetable stock

fresh thyme

salt and pepper

Chef's knife

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Ceramic baking dish

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