Boil the potatoes until soft. Peel and mash them when it is still hot.
In a large mixing bowl, add the mashed potatoes, chopped coriander leaves, chopped green chillies and chaat masala. Check the salt and add more according to taste.
Take a bread slice and apply 2 tablespoon of the mashed potato mixture on it.
Pour the sesame seeds on a plate.
Reverse the bread on which the mashed potato mixture has been applied on the plate with sesame seeds. Lightly press the bread on the sesame seeds, so the potato gets coated with sesame seeds.
Heat a skillet on medium heat and add a dollop of butter.
Now shallow fry the bread upside down with the sesame potato mixture facing downwards in the pan. Fry till the sesame seeds become slightly brownish. This should take around 10 Minutes.
Then flip the bread to the other side and fry for a few more minutes until the bottom is slightly crisp and golden. Serve hot with dips.