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