Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

Wash and cut cauliflower into bite-size florets, slice garlic bulbs in half horizontally, toss everything in olive oil, salt, and cracked black pepper.

Arrange cauliflower and garlic cut-side up on the sheet and roast until tender and golden brown, about 25–30 minutes.

In a soup pot over medium heat, warm a splash of olive oil, add diced onion, and cook until soft and translucent, about 5–7 minutes.

Add roasted cauliflower and squeeze roasted garlic cloves out of skins into the pot, pour in vegetable broth, and add thyme sprigs.

Bring to a gentle boil, then reduce heat and let the soup simmer uncovered for 10–15 minutes.

Remove thyme sprigs, then use an immersion blender to puree the soup until silky smooth.

Stir in lemon juice, taste and adjust seasoning with salt and pepper, and swirl in coconut milk if desired.