01 - Preheat your oven to 400°F. Arrange the parsnip chunks and onion quarters evenly on a large baking sheet. Place the garlic bulb, cut side facing up, on the same sheet. Drizzle all the vegetables generously with olive oil and season with salt and pepper. Toss gently to ensure an even coating.
02 - Roast the vegetables for 30 to 35 minutes, turning the parsnips once halfway through, until they are golden brown and tender. The garlic should be soft and slightly caramelized; if it begins to brown too quickly, cover it loosely with aluminum foil.
03 - Carefully squeeze the softened roasted garlic cloves from their skins into a large soup pot. Add the roasted parsnips and onions to the pot. Pour in the vegetable stock and bring the mixture to a gentle simmer over medium heat. Allow it to cook for 10 minutes to meld the flavors.
04 - Remove the pot from the heat. Using an immersion blender, carefully blend the soup directly in the pot until it is completely smooth and creamy. Alternatively, you may transfer the soup in batches to a standard blender, blending until smooth, then returning it to the pot.
05 - Stir in the heavy cream and ground nutmeg, if you are using it. Taste the soup and adjust the seasoning with additional salt and pepper as needed.
06 - Gently reheat the soup if necessary. Ladle the warm soup into bowls and garnish with chopped fresh herbs and a final drizzle of olive oil or cream.