Step 1

In a medium saucepan, heat oil over medium-high. Add onion, chopped ginger, garlic, and a pinch of salt; cook until softened, 4 to 5 minutes. Add beets, potato, and 4 cups water. Season with salt and pepper. Bring to a simmer, cover, and cook until vegetables are tender, 25 to 30 minutes. Let cool slightly; transfer to a blender. Blend until smooth, adding 1/4 to 1/2 cup water for desired consistency.

Step 2

Stir together yogurt and grated ginger. Ladle soup into bowls; swirl in yogurt. Top with thyme (if desired), a drizzle of olive oil, and more pepper.