01 - Preheat the oven to 400°F.
02 - Arrange parsnip chunks and onion quarters on a large baking tray. Place the garlic bulb cut side up on the tray. Drizzle all vegetables with olive oil and sprinkle with salt and pepper. Toss to coat evenly.
03 - Roast for 30 to 35 minutes, turning parsnips once halfway through, until golden and tender. The garlic should be soft and caramelized; cover with foil if it begins to brown too quickly.
04 - Squeeze the roasted garlic cloves out of their skins into a large soup pot. Add the roasted parsnips and onions to the pot.
05 - Pour in the vegetable stock and bring to a simmer over medium heat. Cook for 10 minutes to allow flavors to meld together.
06 - Remove from heat. Use an immersion blender to puree the soup until completely smooth and silky. Alternatively, work in batches using a standard blender.
07 - Stir in the heavy cream and nutmeg if using. Taste and adjust seasoning with additional salt and pepper as needed.
08 - Reheat gently if necessary. Ladle into serving bowls and garnish with fresh herbs and a drizzle of cream or olive oil.