Remove the seeds from 2 medium-sized custard apples (approximately 500 grams) and scoop out the pulp. Set aside.
In a blender, add the custard apple pulp, 500 ml chilled milk, 2 tablespoons sugar (adjust according to taste), 1/4 teaspoon cardamom powder, and a pinch of saffron strands (optional).
Blend the mixture until smooth and creamy. If the smoothie is too thick, add a little more milk and blend again to achieve the desired consistency.
Pour the smoothie into serving glasses and garnish with a few chopped nuts like almonds or pistachios (optional).
Serve the custard apple smoothie chilled.