Preheat the oven to 375?F.

Put the beets, fennel, 2 tablespoons of the oil, salt, and pepper in a large bowl and toss to combine. Spread the vegetables on a baking sheet covered with aluminum foil and roast until caramelized, 45 minutes to 1 hour.

Remove from the oven and cool slightly. When cool enough to handle, cut into 1/2-inch cubes.

Heat the remaining oil in a saucepan over medium-high heat. Add the onions and cook, stirring, until soft, 3 to 4 minutes. Add the carrots and celery and cook, stirring, until soft, 3 minutes. Add the garlic and cook, stirring, for 30 seconds. Add the fennel, beets, and stock, and bring to a boil. Reduce the heat to medium-low and simmer for 20 minutes. Remove from the heat and cool slightly.

With an immersion blender, or in batches in a food processor or blender, purÈe the soup. Refrigerate the purÈe until cool, at least 2 hours.

In a small bowl combine the sour cream, applesauce, mint, and sage, and stir to combine.

Ladle the chilled soup into serving bowls, top with a dollop of Apple-Mint Crema and pistachios, and serve.