During Saaka Vratha, chillies are not used. Instead pepper powder is added to dishes. Similarly, instead of the regular rasam powder, this cumin-pepper powder is used. This powder is also used to flavor,sambar, lentil stir fry etc.
The trick is frying the cumin and pepper [1:1] with a little ghee on a low flame till the pepper and cumin pop. [A little care has to be taken here as the pepper sometimes 'flies' out of the pan!].The mixture is cooled and ground to a fine powder. Store the powder in an airtight container and use as required.
The reason for using ghee instead of oil is that ghee gives a nice flavor to the powder which in turn makes the dish more flavorful.