Place potatoes in a pot. Add water to cover them. Cook until tender. Peel the potatoes and let to cool completely, as, cold potatoes reduces the percent of falling apart of your kookoo while cooking them. Then, mash cold potatoes with a masher.
Grate the onion and drain the juice. onion juice also can cause kookoo to fall apart while cooking),therefore, drain the juice
Add spices, egg, bread crumbs and grated onion to the mashed potatoes.
Use your hand and mix all ingredients together.
Until we have a well combined paste like. place the potatoes mixture in the fridge for 30 minutes.
After half an hour, Form patties in oval or round shape. then, coat each patty with bread crumbs. Heat the oil in a pan and fry for 4-5 minutes on each side until golden and crispy.
Remove the patties from the pan and drain on paper towel.
Slice tomatoes and pickled cucumber.
Now, for making our sandwich, cut the bread lengthwise, arrange slices of tomatoes and pickled cucumber over the bread and place 2 pieces of kookoo sibzamini (potato patties). Traditionally, no need to anysauce and it is just full of flavour and tasty but if you like, add ketchup, mayonnaise or mustard sauce