Sieve 150 g chickpea flour and ¼ teaspoon turmeric powder into a mixing bowl. Crush ¼ teaspoon ajwain between your palms, then add them too. Finally, pour in 150 ml water and whisk the batter until smooth. You may need an extra 1 teaspoon water to adjust the consistency.
Let the batter rest (covered with a plate) for around 20 minutes, while you make the batata vada.
Make the Batata Vada
Add plenty of water to a large saucepan and bring to a rolling boil over medium-high heat. Once boiling, add 3 medium potato. Boil until tender, then drain. Cool slightly and peel.
Add the potatoes to another mixing bowl, and mash until mostly smooth (some texture is fine).
Heat 2 teaspoon oil in a small tadka pan over low-medium heat. Add ½ teaspoon black mustard seeds and wait for them to pop. Once the pop, immediately add 1 green finger chilli (chopped) and 1 sprig fresh curry leaves. They will splutter, so be careful! Next, add ½ white onion (chopped), and sauté until softened. Then add ¼ teaspoon ginger garlic paste and ¼ teaspoon turmeric powder, cooking until the raw smell has faded. Turn off the heat.
Pour the tadka (tempering) over the mashed potatoes. Sprinkle over sea salt (to taste), ⅛ teaspoon garam masala, and 5 strands fresh coriander (chopped). Mix everything well and form into small patties (this recipe makes six by default, but it' s adjustable).
Make the tamarind chutney by adding 50 ml tamarind paste, 40 g grated jaggery, 50 g pitted dates, sea salt (to taste), ¼ teaspoon cumin powder, ¼ teaspoon fennel powder, ¼ teaspoon red chilli powder, and 1 pinch ginger powder to a small saucepan. Bring to a boil and cook for two minutes, or until the mixture reduces and thickens.
Cool the mixture, then use a hand blender or mixer grinder to puree and pass it through a sieve. Set aside.
Make the dry garlic chutney by heating 1 litre oil in a large kadai or deep fat fryer. Heat the oil to 160℃ (325℉). Once the oil has heated, slowly pour some of the batter through a slotted spoon (you want small pieces), or let it drop from your fingers. Fry the batter bits until golden brown. Drain on a paper towel.
Next, dry roast (without oil) 40 g garlic until blistered. Place them in a blender. Repeat the same dry-roasting process for 1 teaspoon sesame seeds (roasting until aromatic), then 2 tablespoon desiccated coconut. Add these to the blender along with 40 g batter bits (any extra can go in your burgers), sea salt to taste, and 1 tablespoon deggi mirch. Pulse the mixture until it's combined.
Fry the Batata Vada
Dip the potato patties (batata vada) into the batter until fully coated. Carefully lower them into the same oil for deep-frying. Don't overcrowd the pan; fry three at a time, until golden. Remove with a slotted spoon and drain excess oil. Repeat.
If you have any leftover batter, you can make more batter pieces. These are delicious served in the burger or on the side. Once done, turn off the stove or deep fat fryer.
Fry the Green Chillies
Using a knife, score 20 g green finger chillies lengthways to make a small slit. Lower them into the deep frying oil and cook in the residual heat until blistered. Be careful! They can spit oil. Remove and drain excess oil, then sprinkle with fine ground sea salt.
Assemble the Vada Pav
Cut each bread roll into half. Spread coriander chutney on the top half and tamarind chutney on the bottom half. Sprinkle the dry garlic chutney over the tamarind chutney. Next, place a batata vada on top, scatter over batter bits, and close the pav/bread rolls. Serve with fried green chillies on the side (or in the Bombay burger if you prefer!).
Notes
I have made this vada pav less spicy than the traditional Mumbai-style version. You can increase the amount of green chili in the green coriander chutney or deggi mirch in the dry garlic chutney to amp it up a notch.