In a large saucepan, melt the butter over low heat. Add the onions and sugar and sauté for 10 minutes. Add the wine and parsnips and simmer covered for 20 minutes, or until onions and parsnips are tender.
Add stock and bring to a boil. Reduce heat and simmer for 10 minutes. Stir in chickpeas. Cool slightly, then use a submersion blender or food processor and blend until smooth. Season to taste with salt.
Drizzle with cream and garnish with fresh thyme leaves.