Remove the seeds from 2 ripe custard apples and scoop out the pulp. Set aside.
In a blender, add 400 grams of chilled yogurt, the custard apple pulp, 2 tablespoons of sugar, and a pinch of cardamom powder. Blend until smooth and creamy.
If the lassi is too thick, add 100 ml of chilled water or milk and blend again to achieve the desired consistency.
Pour the custard apple lassi into glasses and garnish with a few chopped nuts like almonds or pistachios, if desired.