Wash and peel 500 grams of potatoes. Cut them into 2 cm cubes and place them in a large pot. Add enough water to cover the potatoes and bring it to a boil. Cook the potatoes for 10-15 minutes or until they are tender but not mushy. Drain the potatoes and let them cool completely.
In a large mixing bowl, combine 100 grams of thick yogurt, 50 grams of mayonnaise, 1 tablespoon of lemon juice, 1 teaspoon of mustard sauce, salt, and black pepper to taste. Mix well to create a smooth dressing.
Finely chop 1 small onion, 1 small cucumber, and a handful of fresh coriander leaves. Add these to the cooled potatoes.
Pour the dressing over the potato mixture and gently mix until all the ingredients are well coated.
Cover the bowl and refrigerate the potato salad for at least 1 hour to allow the flavors to meld together. Serve chilled.