1. Heat oil in a medium heavy-bottomed pot over medium heat. Add shallots; season with salt and pepper. Cook, stirring, until translucent, about 5 minutes.

2. Add celery root, milk, 2 cups water, bay leaf, garlic, and nutmeg. Season with salt and pepper. Bring to a boil. Reduce heat; simmer until celery root is very tender, about 15 minutes. Let cool.

3. Discard bay leaf. Transfer solids to a blender using a slotted spoon. Add 1/4 cup cooking liquid. Blend until smooth (add more cooking liquid, if needed). Season with salt and pepper.