Curried Carrot and Apple Soup

Name: Curried Carrot and Apple Soup
Ingredients: 4 tablespoons unsalted butter; 1 medium onion, chopped; 1 medium leek, halved lengthwise and thinly sliced crosswise; 1 medium fennel bulb, cored and chopped; Kosher salt; Pepper; 2 pounds carrots, cut crosswise into 1/4-inch rounds; 1 1/4 pounds celery root, peeled and chopped; 1 Granny Smith apple, peeled, cored and chopped; 7 gingersnap cookies; 1 tablespoon Madras curry powder; 2 garlic cloves, crushed; 1 teaspoon finely grated peeled fresh ginger; 2 thyme sprigs; 2 quarts chicken stock; 1 cup sour cream; 1 teaspoon apple cider vinegar; Toasted pumpkin seeds, for garnish; Chopped mint, for garnish; Chopped cilantro, for garnish