Add the cauliflower and a pinch of salt to a boiling pot of water and cook until cooked through and very tender, about 10 minutes. Drain well and quickly dry well with paper towels. Add the hot cauliflower to a food processor with the chicken stock, cheese, olive oil, yogurt and garlic and process until smooth. Stir in a pinch of salt and pepper and the chopped rosemary, and serve immediately.