01 - Preheat oven to 425°F (220°C).
02 - Toss sliced fennel and diced potatoes with 1 tablespoon olive oil, salt, and pepper. Spread on a baking sheet and roast for 25–30 minutes, stirring halfway, until golden and tender.
03 - While the vegetables roast, heat remaining 1 tablespoon olive oil in a large pot over medium heat. Add chopped onion and cook for 5–7 minutes until soft and translucent. Add garlic and thyme; sauté 1 minute until fragrant.
04 - Add roasted fennel and potatoes to the pot. Pour in vegetable broth. Bring to a boil, reduce heat, and simmer for 10 minutes.
05 - Remove from heat. Using an immersion blender (or in batches in a blender), blend the soup until smooth and creamy.
06 - Stir in heavy cream (or coconut milk) and a pinch of nutmeg. Reheat gently if needed. Taste and adjust seasoning.
07 - Ladle into bowls. Garnish with fennel fronds and a drizzle of cream or olive oil.