Before assembling your Aloo Raita, preparing the yogurt base is essential for a rich, thick consistency.
Make sure that neither potatoes nor yogurt feature heavily in the other dishes on your menu to maintain a balanced meal.
Line a colander with three thicknesses of cheesecloth (about 16 inches/40 cm square) or a clean white handkerchief.
Place the 2 cups (16 oz / 454g) of plain yogurt in the cloth, gather up the four corners, and tie it closed with a piece of kitchen twine. Hang the yogurt where it can drip—such as from a kitchen cabinet knob or a sink faucet—and let it drain into a bowl or sink for 2–3 hours.
Place the drained, condensed yogurt into a 1-quart bowl and stir with a fork until perfectly smooth and creamy. Gently fold in the cubed potatoes.
Heat the 1 tbsp (0. 5 oz / 14g) of ghee or vegetable oil in a small pan over moderately high heat.
When the oil is hot but not smoking, add the 1 tsp (0. 1 oz / 3g) of black mustard seeds and the slivered green chilies.
Fry the mixture until the mustard seeds pop and turn gray.
Let it Rest: While you can serve this dish immediately at room temperature, chilling your Aloo Raita in the refrigerator for 1 to 2 hours allows the spices, green chilies, and herbs to beautifully meld with the creamy yogurt.