How to Make It
Preheat oven to 425°F. Toss together beets, potato, 2 tablespoons oil, 1 teaspoon salt, and ½￼ teaspoon pepper on a rimmed baking sheet. Roast until beets and potato are tender, 35 to 40 minutes.
Heat remaining 1 tablespoon oil in a large saucepan over medium-high. Add leek and remaining ¼￼ teaspoon each salt and pepper; cook, stirring, until tender, about 4 minutes. Add broth, beets, potato, and thyme; bring to a simmer and cook, mashing occasionally with a potato masher, for 10 minutes. Stir in vinegar. Garnish with crème fraîche and pumpkin seeds. Serve with bread on the side, if desired.