How to Make It
Combine pumpkin seeds, cumin, and 1 1/2 teaspoons oil in a bowl; toss to coat. Heat a large nonstick skillet over medium-high. Add pumpkin seed mixture to skillet, and toast, stirring often, until lightly browned, 2 to 3 minutes. Set aside.
Heat remaining 1 1/2 tablespoons oil in a large saucepan over medium-high. Add onion, thyme, and garlic. Cook, stirring occasionally, until softened, 5 to 6 minutes. Add turmeric, and cook, stirring constantly, 1 minute. Remove from heat.
Whisk together flour and 1/2 cup stock in a small bowl until smooth. Add flour mixture, salt, cauliflower florets, and remaining 2 cups stock to onion mixture in saucepan. Increase heat to high, and bring to a boil, stirring occasionally. Reduce heat to medium-low, and simmer, covered, until cauliflower is very tender, about 15 minutes.
In batches, place soup in a blender. Remove center piece of blender lid (to allow steam to escape); secure lid on blender. Place a clean towel over opening in lid. Process on high until smooth. Return soup to pot. Stir in vinegar, brown sugar, and pepper.
Serve in bowls; top evenly with pumpkin seeds, sour cream, and chives.