Combine the first 5 ingredients in a small bowl then set aside.
Place the olive oil in a large pot over medium heat. Once warm add the onions and garlic then cook until the onions are soft, about 6 minutes.
Add the ginger, additional nutmeg and 1¼ teaspoons of the spice mixture that was set aside in the first step. Cook for 1 minute.
Add the sweet potatoes and vegetable broth then cover and bring the mixture to a boil over medium-high heat. Once boiling, reduce the heat to medium-low. Stir in the applesauce then let simmer, covered, on medium-low for 20 minutes.
When the potatoes are tender, puree the mixture until smooth with an immersion blender or food processor. Season with salt and pepper to taste. Keep warm while you prepare the spiced butter.
In a small skillet over medium heat melt the butter then add the remaining ¼ teaspoon of the spice mixture. Stir over the heat until browned, just a couple minutes, then remove from the heat. Mix in the apple cider vinegar then drizzle over each serving of soup.
Notes
If you are using curry powder instead, substitute 1.5 teaspoons curry powder for the first 5 ingredients.
Recipe by Lemon & Mocha at http://www.lemonandmocha.com/2014/09/24/spiced-sweet-potato-apple-soup-2/