Melt butter in a large soup pot over medium heat until it stops foaming.
Add garlic and cook until just fragrant. Add onion and shallot and cook until just tender.
Add parsnips and apples and cover with vegetable stock.
Bring to a boil, then reduce to a simmer. Cook until parsnips and apples are fork tender.
Remove from heat and puree with an immersion blender.
Finish with cream and add salt to taste. Keep warm over low heat.