Melt the butter in a large saucepan over medium heat. Fry the onion in butter until soft, about 5 minutes. Add the parsnips, garlic and curry powder, and fry for a couple of minutes to release the flavors. Mix the bouillon cube into the boiling water, and pour into the saucepan. Stir to remove any bits of vegetable from the bottom of the pot. Simmer for 15 minutes or until parsnips are soft and easy to break with a wooden spoon.
Remove from the heat, and blend with a hand mixer or immersion blender. Stir in the cream, and heat through. Do not boil. Season with salt and pepper to taste, and garnish with red pepper flakes or paprika.