Mix ragi flour, rice flour and soya flour in a bowl. Add butter and mix with your fingertips till the mixture resembles breadcrumbs.
Add sesame seeds, cumin seeds, ginger-green chilli paste, yogurt, salt and mix well. Add sufficient water and knead to a soft dough.
Put small portions of the mixture into a chakli mould and press out several chaklis onto a plastic sheet. Heat sufficient oil in a kadai till moderately hot.
Gently slide in the chaklis and deep-fry till light golden brown and crisp. Drain on absorbent paper and set aside to cool. Store in an airtight container and serve them when required.