INGREDIENTS

• 1 tablespoon unsalted butter
• 6 small shallots, finely sliced
• 1/4 pound potatoes, peeled and cubed
• 1 3/4 pounds celery root, peeled and cubed
• 2 tablespoons chopped fresh thyme
• Salt
• Freshly ground black pepper
• 5 cups vegetable broth
• Grated Gruyère, for serving

PROCEDURE

In a large stockpot, melt the butter over medium heat until frothy.  Add the shallots, and cook on medium-low to medium heat until caramelized, about 10 minutes.  Keep a cup of water on the side, and add a splash every few minutes to keep the shallots from burning before they are caramelized.

Add the potatoes, celery root, thyme, salt, pepper, and vegetable broth, and bring to a boil over high heat.  Cover, and reduce the heat to medium-low, simmering for 30 minutes.  Add the contents of the pot to a blender, and carefully purée until smooth.  Serve very hot, with a big pile of coarsely grated Gruyère to pile on top and melt into the soup.