Soak the red chillies in the warm water for sometime.
Meanwhile, chop the coriander and add it to a blender along with the other coriander chutney ingredients and blend till smooth.
Keep the coriander chutney aside and drain the red chillies.
Now add the chillies into another blender along with the other garlic chutney ingredients except the lemon juice and blend till you get a smooth paste.
Mix in the lemon juice and set the chutney aside.
Begin making the sandwich by spreading 1/2 tbsp of butter on both slices.
Spread both the chutneys as per how spicy you like your sandwich.
Place the boiled potato slices, tomato slices, onion slices and the beetroot on one of the slices.
Season with the chaat masala and salt.
At this point you can add the grated cheese on the inside but Mumbai street sandwich vendors put it on top of the grilled sandwich.
Cover the stuffed slice with the second one and apply butter on the outer surfaces of the bread slices.
Now place the sandwich in a jaffle maker or a regular electronic grill and cook till you get a brown, crisp bread on both sides.
Place the sandwich on a plate, slather with butter and grated cheese and cut it into six equal pieces using a sharp knife.
Serve with a dollop of both the chutneys on the side.