Combine the 2. 0 cups (16. 0 oz / 455g) plain yogurt (or the yogurt and sour cream blend), 0. 75 tsp (0. 1 oz / 3. 5g) salt, and 0. 125 tsp (0. 01 oz / 0. 5g) white pepper in a large mixing bowl, whisking vigorously with a fork until the base for your Tamatar Raita is completely smooth and creamy.
Wash and dry the 1. 0 lb (16. 0 oz / 455g) tomatoes, cut them into 0. 5-inch cubes (or quarter them if using cherry tomatoes), and gently drop them into the smooth yogurt mixture without stirring, leaving it ready to be covered and refrigerated for several hours or assembled immediately at room temperature.
Heat the 1. 0 tbsp (0. 5 oz / 15g) vegetable or peanut oil in a small pan over moderate heat until it is hot but not smoking, then carefully add the 1. 0 tsp (0. 1 oz / 5g) black mustard seeds and the minced green chili, frying them until the seeds crackle and turn a grayish color.
Pour the hot spiced oil directly into the bowl to temper the Tamatar Raita, gently blend everything together to distribute the flavors, and serve immediately with a beautiful garnish of fresh coriander, basil, or dill sprigs.
Whisk for Silkiness: Don't skip whisking the yogurt! Vigorously whisking the plain yogurt (or yogurt and sour cream blend) before adding the tomatoes breaks down any lumps and creates a luxurious, velvety mouthfeel.