Apply butter on four bread slices. Arrange potato slices and onion rings on each. Sprinkle two tablespoons of grated cheese, salt, chaat masala and red chilli powder on each.
Cover with remaining bread slices. Apply some more butter on them and toast in a sandwich toaster till evenly done on both sides.
Sprinkle half tablespoon dry vada pav chutney on each sandwich and serve hot.