Place the mashed potatoes in a bowl
Add all other ingredients (except bread and butter) to this and mix well
Taste test this mixture to make sure you are happy with the spice, sourness, and salt levels
Remove the crust from the bread slices, if you'd like
Take one slice and butter a side generously
Place about 2 tbsp (or more) of the aloo masala on the buttered bread slice
Cover with another slice and butter the top of this slice
Heat up your griddle or tawa
Place the sandwich, buttered side down on the heated pan
Butter the other side now
Press down gently with a spatula and grill the sandwich until both sides are crispy and golden brown
Cut the sandwiches diagonally and serve warm with Sriracha chilli sauce (our favourite) or tomato ketchup