Preheat oven to 425°F and line a baking sheet with parchment paper.
Toss cauliflower florets with 1 tablespoon olive oil, salt, and pepper, then spread on baking sheet and roast for 30-35 minutes until golden brown.
In a large pot, heat remaining olive oil over medium heat and sauté onion until softened, about 5 minutes, then add garlic and cook for 1 minute more.
Add roasted cauliflower, vegetable broth, and thyme to the pot and bring to a boil, then reduce heat and simmer for 10 minutes.
Use an immersion blender to puree soup until smooth, or carefully transfer to a blender in batches.
Stir in almond milk and adjust seasoning with salt and pepper before serving.