Boil the potatoes a day before and refrigerate them overnight or at least for 3 to 4 hrs. But remember only refrigerate them if you have boiled them over stove top or in pressure cooker.If you have cooked them in microwave then let then cool down on counter top for an hour.
Pulse the panko crumbs in a mixed couple of times. Panko crumbs are larger in size and hence we need to grind it to make a finer crumbs.
Chop all the vegetables and blanch the carrots, beans and peas in hot water for 2 to 3 minutes. then drain them.
Chop the yellow onion and soak them in hot water for 10 mins.
Soak the poha in water and drain them. Keep them aside for later.
Peal and mash the potatoes.
Heat up a pan and add unsalted butter to it.
To the butter add the onions, sauté them for 3-4 minutes.
Once they are translucent and cooked add the other blanched vegetables. Cook them for about 3-4 minutes.
Now add the mashed potatoes to the veggies and mix it in. Add salt and mix again.
Once all comes together add all the dry spices and mix everything together. Switch off the flame.
To this mixture add the soaked and mashed poha and mix it all together with a potato masher. This will help in binding of the patty.
Take a cling wrap, place the patty mixture on it and roll it into a tight log. Squeeze it tight and roll it well.
Place this roll in a zip lock bag and freeze it for about 20 minutes. This will firm up the roll and make it easier to cut.
Make the batter with all purpose flour, corn starch, corn meal, salt, black pepper powder, ice cold water and oil.
Cut the roll into patties and press and shape them as per the burger bun size.
Heat up the oil for frying. The ideal temperature for frying is 350F - 365F.
Dip the patty in the batter, drain the excel liquid.
Then coat it with bread crumbs.
Fry this patty in oil till it turns golden brown from each side.
Remove the patty on a paper towel. The patty will be crisp from outside.
The the burger bun and split it in half. brush it with butter and toast it in the pan.
Place the patty on burger bun, top it with shredded lettuce and mayonnaise and serve it hot.
Notes
You can replace panko bread crumbs with any other bread crumbs available.
You can replace cornmeal with powdered cornflakes in case you are not able to find corn meal.
Unsalted butter can be replaced with any other good oil.