1) Wash the red kidney beans under cold running water until the water runs clear or rinse them until the water is no longer cloudy.
Soak them in water (at least 9 cm above the beans) – for at least 8 hours or overnight. Or go for a quick soaking method: Add kidney beans and water (at least 6 cm above the beans) to a saucepan. Let it come to a boil on medium heat. Once it starts boiling, turn off the stove, cover it and let it sit for 1 hour.
2) Drain the soaking water. Add 500 ml of water and cook the beans.
Instant pot: Pressure cook (manual) high pressure 8-10 minutes.
Stove-top: simmer for 30-40 minutes. You may need more water.
Stove-top pressure cooker: 1 whistle on high heat, then lower the heat and cook for 10 minutes.
3) While the beans are cooking, boil the sweet potato. You can even cook both the beans and sweet potato at the same time in the instant pot. Alternatively, you can oven roast the sweet potato slices.
4) Drain the cooked beans completely. Make sure to get rid of all the water and the beans are as dry as possible. Mash them with a fork or potato masher.
5) Peel and mash the sweet potato. Measure it to 250 ml and keep it aside.
6) Heat the 1 tablespoon of oil in a pan on medium heat.
7) Once hot, add chopped onions, green chilies, and minced ginger. Sprinkle a little salt to speed up the process.
8) Stir and cook until the onion becomes soft and light pink.
9) Add spices (turmeric powder, red chili powder, and garam masala).
10) Mix well and cook for 30 seconds. Then turn off the stove. Let the mixture cool down slightly.
11) Take mashed kidney beans and sweet potatoes in a bowl.
12) Add cooked onion mixture, cilantro, lime juice, and remaining salt.
13) Mix and add breadcrumbs, using best judgment on how much to add. The mixture should come together like a dough ball. It should not be too soft or too sticky.
14) Divide the mixture into 6 equal portions to get a really thick patty or 8 portions for medium thickness patty.
15) Use your hand to give a round shape. Also, seal the sides and make sure there are no cracks.
16) Heat a generous amount of oil in a cast-iron skillet on medium-low heat. TIP: Please use a good amount of oil. These are a vegetarian burgers, so they need more oil, unlike the meat burger patty which already have fat in them.
17) Once golden brown and slightly crisp from the bottom, flip and cook the other side.
It is very important to cook them on medium-low heat to ensure an even browning without burning or creating a crust. This is not a meat patty that you have to worry about over-cooking and drying the texture. Take your time and make it perfect.
Mix thick yogurt (or Greek yogurt) with hot sauce. This goes well with the slight sweetness of the sweet potatoes. Of course, you can choose any other sauce you like. For the topping, you can go for classic onion, tomato, lettuce, or avocado.