Step 1

In a large heavy saucepan, melt 2 tablespoons of the butter over medium heat

Step 2

Add the shallots and saute for about 2 minutes, or until translucent

Step 3

Add the celery root, broth, milk, cream, 2 of the thyme sprigs, the bay leaf and salt and bring to a gentle simmer

Step 4

Reduce the heat to medium-low and simmer very gently, uncovered and stirring occasionally, for about 35 minutes, or until the celery root is tender enough to mash with a spoon

Step 5

Remove from the heat and remove the thyme sprigs and bay leaf

Step 6

Working in batches and using a slotted spoon, transfer the celery root and shallots to a blender (preferably a high-powered one) and blend until smooth, adding enough of the cooking liquid to form a smooth and creamy soup (you may not need all the liquid)

Step 7

Return the pureed soup to the pot and rewarm over low heat before serving

Step 8

Just before serving, in a small skillet over medium heat, swirl the remaining 2 tablespoons butter for about 3 minutes, or until melted and golden brown

Step 9

Remove from the heat

Step 10

Ladle the soup into bowls

Step 11

Pluck the leaves off the remaining 2 thyme sprigs and sprinkle the leaves over the soup

Step 12

Drizzle with the browned butter and serve