How to Make It
Preheat the oven to 500°. On a large rimmed baking sheet, toss the beet, turnip, parsnip and onion with the olive oil and spread in a single layer. Roast the vegetables for about 20 minutes, stirring once or twice, until tender and golden brown around the edges.
Transfer the vegetables to a large saucepan. Add the stock; cover and bring to a boil. Simmer over low heat until the vegetables are tender, about 10 minutes.
Working in batches, puree the soup in a blender or food processor until smooth. (Alternatively, use an immersion blender to puree the soup.) Return the soup to the saucepan and reheat gently. Season with salt and pepper. Ladle the soup into deep bowls. Top with a dollop of crème fraîche and the chopped fresh dill and serve at once.