Roasted beets add sweetness and a rich red color to this satisfying autumn soup; reserve the beet greens for Sautéed Fall Greens with Caraway. The texture of the soup should be thick and not completely smooth.
1 head of garlic, top sliced off to expose the cloves
1 tablespoon water
1 pound carrots, cut into 1-inch pieces
1 pound turnips, cut into 1-inch wedges
2 medium onions, quartered
1/4 cup plus 1 tablespoon extra-virgin olive oil
Freshly ground pepper
16 thin baguette slices
7 cups chicken stock or canned low-sodium broth
1 cup finely chopped mint
Preheat the oven to 400°. Put the beets and garlic on a large piece of foil and sprinkle with the water. Wrap the beets and garlic in the foil and roast for about 1 hour, or until the beets are tender when pierced with a knife and the garlic feels soft when pressed. Let cool slightly. Peel and quarter the beets and put them in a large bowl. Squeeze the soft garlic cloves from their skins onto the beets.
Meanwhile, on a large rimmed baking sheet, toss the carrots, turnips and onions with 1 tablespoon of the olive oil and season with salt and pepper. Spread the vegetables in a single layer and roast for about 1 hour, stirring occasionally, until tender and browned. Add the roasted vegetables to the beets.
Arrange the baguette slices on another baking sheet and bake for about 3 minutes, or until toasted.
Working in batches, coarsely puree all of the roasted vegetables in a food processor, adding enough chicken stock to loosen the mix. Transfer the puree to a saucepan, add the remaining chicken stock and bring to a simmer over moderate heat. Season with salt and pepper.
In a small bowl, stir the remaining 1/4 cup of oil into the mint and season with salt and pepper. Spoon the mint onto the toasts. Ladle the soup into bowls and serve with the mint croutons.
The soup can be refrigerated overnight and the toasts can be stored in an airtight container. Rewarm the soup before serving.