Place cauliflower and garlic on prepared baking sheet. Drizzle with 2 tablespoons olive oil. Season with salt and pepper.
Bake at 350° for 30 minutes, mixing occasionally.
Meanwhile, in a stockpot, mix onion and remaining olive oil and simmer until onion is translucent; should take about 15 minutes on low heat.
In a blender mix both cauliflower and onion mixtures with chicken broth. Blen until pureed or desired consistency.
Put blended soup back into a stockpot to simmer for another 15 minutes, until heated through.
NOTE: You may skip the blender step if you desire a more textured soup.