Stirring constantly, heat the oil along with ginger, turmeric, garlic and ground spices in a large pot over medium heat until fragrant (about 2 minutes). Do not brown.
Add carrots and salt, stir to coat. Add water, bring to a boil, then lower to a simmer and continue to simmer until carrots are tender, (about 20-25 minutes).
Puree soup in a high speed blender until smooth. Return to pot if necessary to gently re-heat before serving. Serve hot with yogurt and freshly ground pepper to top if desired.
