Sauté aromatics: In a large pot, heat oil or ghee over medium heat. Add the onion and garlic and cook until softened, about 5 minutes.
Add spices: Stir in turmeric, cumin, and black pepper. Let cook for about 30 seconds to release their aroma.
Cook the vegetables: Add the potatoes (and carrot, if using). Stir to coat everything in the spice mixture.
Add broth and simmer: Pour in the vegetable broth and bring to a boil. Reduce heat and simmer gently for 20–25 minutes, or until the potatoes are soft.
Blend: Use an immersion blender to partially or fully puree the soup, depending on your texture preference. You can also blend just half of it for a mix of creamy and chunky.
Season and finish: Taste and adjust salt. For extra richness, stir in a splash of cream or coconut milk just before serving.
Serve: Ladle into bowls and top with chopped herbs. Serve with crusty bread or roti.