In a blender, add 250 grams of chilled plain yogurt (dahi), 1/2 teaspoon of black salt (kala namak), 1/2 teaspoon of roasted cumin powder (bhuna jeera powder), and 1/4 teaspoon of black pepper powder (kali mirch powder).
Blend the ingredients until smooth and frothy.
Add 150 ml of chilled water to the blender and blend again for a few seconds to mix well.
Taste the lassi and adjust the salt and spices according to your preference.
Pour the salted lassi into glasses and garnish with a pinch of roasted cumin powder and a few mint leaves (optional).
Serve the salted lassi chilled.