In a large bowl, take 500 grams of chilled, thick curd (yogurt) and whisk it until smooth.
Add 4 tablespoons of sugar (adjust according to taste) and mix well until the sugar dissolves completely.
Add 1/2 teaspoon of cardamom powder and mix well.
Gradually pour in 250 ml of chilled water or milk, while continuously whisking the mixture to achieve a smooth and creamy consistency.
Optionally, you can add a few strands of saffron soaked in 1 tablespoon of warm milk for added flavor and color.
Pour the sweet lassi into serving glasses.
Garnish with a pinch of cardamom powder or chopped nuts like almonds or pistachios, and serve chilled.