Peel the boiled potatoes and mash them while still warm.
Add the remaining ingredients to the mashed potatoes and mix well. Taste seasoning and adjust accordingly.
Cut the bread into triangular pieces. Put a layer of mashed potatoes on one piece of bread. Cover with another. Make sandwiches like these with remaining slices. Keep aside.
In a wide bowl, put besan. Add hing, garam masala powder, red chilli powder, salt, carom seeds, chopped coriander leaves. Add about 1/2 cup of water. The consistency should be neither thick nor thin. Check seasoning and adjust if needed.
Pour oil in a kadai and let it heat on a flame. Once hot, reduce to mid flame.
Take one set of the sandwich and dip into the besan batter so it coats beautifully. Let it slide into the kadai.
Fry till it is crisp and golden brown. Drain on tissue paper.