Heat the large pot over medium heat and add the olive oil. Once shimmering, add the diced onion and sauté until translucent and fragrant, about 5 minutes.
Add the minced garlic to the pot and cook for another 30 seconds, until fragrant, being careful not to burn it.
Stir in the chopped carrots, parsnips, and sweet potato, coating them with the aromatic mixture. Cook for about 5 minutes, allowing the veggies to begin softening and release their flavors.
Pour in the vegetable broth, scraping any bits off the bottom of the pot. Bring the mixture to a gentle simmer and cover with a lid.
Let the soup simmer for about 20-25 minutes, or until all the root vegetables are tender when pierced with a fork.
Add the chopped kale and sprinkle in the ground cumin if using. Stir well, and cook for another 5 minutes until the kale wilts and brightens the soup.
Taste the soup and season with salt and freshly ground black pepper as needed.
Remove from heat and ladle the soup into bowls. The vegetables should be tender and the broth flavorful and slightly thickened.
Finish with a squeeze of lemon or a drizzle of olive oil if desired, and enjoy immediately while warm and hearty.
