Heat a large pot or dutch oven over medium heat, then add the beef. Cook the beef, breaking it up with a wooden spoon. Once cooked, remove with a slotted spoon, then drain all of the fat from the pot.
Add the oil to the pot, along with the onion, carrots, celery, and garlic and sauté until soft, about 5 minutes. Then, add the salt, potatoes, cauliflower, and chicken broth.
Bring the soup to a boil, then reduce to a simmer and simmer until the potatoes are soft, 10-15 minutes.
Use a slotted spoon to remove the cauliflower and HALF of the potatoes and transfer them to a blender. Add the milk and blend until smooth, then pour back into the pot. As this point you should add the cooked beef back in as well.
Add the yogurt, then use a whisk to whisk until smooth. Then, add the cheese and continue whisking until the cheese has melted.
Divide the soup into bowls, then garnish with fresh chives and more cheese. Enjoy!