Preheat oven to 200°C. Cut potato into thin slices.
Mix onion and salt in a bowl. Add potato, carom seeds, coriander leaves, mint leaves, red chilli powder, turmeric powder, cumin powder, gram flour, rice flour and baking soda and mix gently.
Add 3 tbsps water and mix again. Add lemon juice and mix well.
Place silicon moulds on baking tray and grease each of them with few drops of oil. Put spoonfuls of potato-onion mixture in them and place the tray in the preheated oven. Bake for 20 minutes.
Serve hot with your choice of chutney.