Add the cauliflower to a medium-sized saucepan along with the chicken stock. Bring to a simmer over medium-high heat and cook until tender, about 8 to 10 minutes. Add the roasted garlic and season with salt and pepper, to taste. Stir in the milk and puree with an immersion blender until smooth. Mix in the cheese and taste for seasoning. Transfer the mixture to a serving bowl and garnish with sour cream and chives.