Preheat oven to 425ºF. Line a baking sheet with parchment paper. In a large bowl, toss sweet potatoes, parsnips, shallots, garlic, olive oil, ½ tsp salt and cumin together. Pour onto prepared baking sheet and roast 30 minutes, stirring after 15 minutes. Remove from oven and set aside.
In a large soup pot, bring vegetable broth and apple cider to a boil over medium-high heat. Add sweet potato mixture and simmer for 10 minutes. Remove from heat and using a handheld or countertop blender, puree until smooth. Return to soup pot over medium heat and stir in butter, ¼ tsp salt and pepper. Garnish each soup bowl with diced apple and parsley.