Preheat the oven to 200°C (400°F). Scrub the parsnips and carrots, then top and tail them. There's no need to peel these vegetables. Cut into rounds about 2cm (¾ in.) in size and add to a large baking dish.
300 grams parsnips, 300 grams carrots
Peel the onion and cut into thick strips. Add to the baking dish with the garlic, oil, herbs, salt, and pepper.
Roast for about 40 minutes, or until lightly golden and softened. Try not to have cut ends of onion sticking up as it might burn at the thinnest parts.
Once the vegetables have cooked, cool slightly before removing the garlic cloves from their skin. Transfer everything to a large pot and add the vegetable broth. Mix with an immersion blender until smooth.