Bring the milk to a boil in a deep non-stick pan. Lower the heat and simmer, stirring continuously, till it reduces by half.
Add the rice flour, mixed with a little water, and stir well to prevent lumps from forming. Bring the mixture to a boil.
When it starts to thicken, lower the heat and simmer for a couple of minutes, stirring continuously. Add the cardamom powder and saffron, and mix well.
When the mixture attains a thick custard-like consistency, remove from heat and stir in the sugar substitute.
Pour the mixture into four individual earthenware bowls while still warm. Sprinkle sliced pistachios and refrigerate for at least two hours.Serve chilled.