Cut 1 quarter from one of the apples.Wrap the unpeeled quarter in plastic wrap and reserve. Peel, core, and quarter the rest of the apples. Chop the peeled apples into 1/2-inch pieces and toss with the lemon juice in a medium bowl.
Heat the olive oil in a heavy-duty 4-quart saucepan over medium-low heat. Add the leeks and onion and cook, covered, stirring occasionally with a wooden spoon, until just tender, 6 to 8 minutes.
Stir in the ginger, tomato paste, garlic, and curry powder and cook, stirring, until fragrant, about 1 minute. Add the vermouth and cook, uncovered, stirring occasionally, until the liquid has almost evaporated, 2 to 3 minutes.
Add the chopped apple, parsnips, and potatoes and stir to coat well. Add the chicken broth and 1-1/2 tsp. salt and bring to a boil over medium-high heat, stirring occasionally. Reduce the heat to medium low, partially cover, and simmer, stirring occasionally, until the apples and vegetables are very tender, about 30 minutes.
In a blender, purée the soup in batches until completely smooth. Transfer the soup to a clean 4-quart saucepan, stir in the cream, and season to taste with salt and white pepper. Bring the soup to a simmer over medium heat, stirring often. Cut the reserved apple quarter into small dice. Serve the soup sprinkled with the diced apple and chives.
The soup can be made 2 days ahead and kept covered and refrigerated. Reheat it gently and garnish just before serving.