In a large soup pot set over medium-high heat, cook the bacon until crisp, about 6 minutes. Transfer the bacon to a paper towel, leaving 1 tablespoon of rendered bacon fat in the pot. Crumble the bacon and set aside.

Reduce heat to medium and add the shallot and garlic. Cook 1-2 minutes, or until softened. Add the potatoes and cauliflower. Sprinkle the flour into the pot; mix well. Slowly stir in the vegetable stock. Bring to a rapid simmer; cover and cook 30 minutes, or until the potatoes are soft.

Working in batches if necessary, transfer the soup to a blender and blend until smooth. Return the soup to the pot and stir in the yogurt. Stir half of the bacon, scallions, and cheese into the soup. Season to taste with salt and pepper.

Serve topped with remaining bacon, scallions, and cheese.