Cut off the top of the garlic head to expose the cloves.
Drizzle with olive oil and wrap in foil
Place cauliflower florets on a large baking pan.
Drizzle with oil, and set the garlic packet on the pan too.
Bake in a 350 degree oven for about 1/2 hour.
Saute onion in olive oil in a large pot for 3-5 minutes until softened.
Squeeze the garlic out from the skins into the pan
Add cauliflower and broth.
Add salt, black pepper and red pepper flakes.
Using an immersion blender, puree the cauliflower or transfer it to a blender and then back to the pot.
Add spinach.
Bring to a boil then reduce heat to low and simmer for 10 minutes.