Preheat oven to 425°F; line baking sheet with parchment.
Toss cauliflower with 1 tablespoon oil, salt, and pepper; spread on sheet and roast 30-35 minutes until golden brown.
Heat remaining oil in large pot over medium; sauté onion about 5 minutes until softened. Add garlic; cook 1 minute more.
Add cauliflower, broth, and thyme; boil, reduce heat, and simmer 10 minutes.
Puree smooth with immersion blender, or carefully transfer to blender in batches.
Stir in almond milk; adjust salt and pepper before serving.