Preheat oven to 425º F. In a large bowl, toss cauliflower with 2 tablespoons of olive oil, 1 teaspoon of salt and pepper. Wrap garlic cloves in foil. Place cauliflower and garlic on a large baking sheet in a single layer and roast for 15–20 minutes, until browned and slightly tender.
Meanwhile: Cook onions with remaining olive oil in a pan over medium-high for 6 minutes, or until fragrant. In batches blend roasted cauliflower, garlic, onion and chicken stock until pureed. In a large pot combine pureed mixture, ½ teaspoon of salt, and half and half. Bring to a low boil, then reduce heat and simmer covered for 15 minutes.
Substitutions/Dietary Restrictions: This recipe is gluten-free. For vegetarian use vegetable stock, and for vegan omit half and half.