Preheat oven to 400°F.
Prep the veggies:
Halve tomatoes and place cut-side up on a baking sheet.
Add onion quarters.
Drizzle everything with olive oil and sprinkle with salt, pepper, thyme, and red pepper flakes.
Place the garlic head on the pan and drizzle lightly with oil.
Roast for 35–40 minutes, until tomatoes are blistered and caramelized and garlic is soft.
Blend:
Squeeze roasted garlic cloves out of their skins.
Transfer tomatoes, onion, garlic, and juices to a blender.
Add broth and blend until smooth.
Simmer:
Pour into a pot and simmer on low for 10–15 minutes.
Stir in cream or coconut milk if using.
Finish & serve:
Taste and adjust salt.
Add torn basil right before serving.