Cook 1 chopped shallot and 1 tablespoon minced ginger in 2 tablespoons butter in a saucepan over medium-high heat until softened, 3 minutes. Add 1 diced peeled sweet potato, 1/2 diced peeled green apple, 1/2 teaspoon Madras curry powder, 3 tablespoons maple syrup and 2 1/2 cups water. Simmer until the sweet potato is tender, 15 to 20 minutes, then puree in a blender until smooth; thin with water if needed. Season with salt and pepper. Pour into 8 to 10 small glasses. Whisk 2 tablespoons each marshmallow cream and heavy cream; drizzle on the soup and top with more diced green apple.