Soak Lentils: Combine lentils in a small bowl. Wash until the water runs clear, then drain the water. Add water for soaking (3/4 cup for 1 batch, 1 1/2 cup for double batch, 2 1/4 cup for triple batch). Cover and allow to soak at room temperature for at least 8 hours, up to 24 hours.
Prepare Batter (Blend): Strain the dals very well, reserving the dal water. Add dals to a blender (See Note 1) along with 1/4 cup the reserved dal water (1/2 cup for double batch, 1/2 cup + 1.5 tbsp for triple). Add garlic, ginger, red chili powder, and salt. Process for 2-3 minutes, stopping to scrape the sides or distribute, until it’s smooth with no dal kernels. It should form a thick, smooth, barely pourable paste, thicker than pancake batter. If it’s having trouble blending and needs more water to grind, add another 1 tablespoon of reserved water and blend again until smooth. (Do not add more water than this – it can lead to a watery batter and cause doughy bhallas that won’t cook through.)
Whisk Batter: Transfer to a bowl or the bowl of a stand mixer with a fitted whisk attachment (or just whisk right in your blender). Add cumin seeds and baking powder (1.5 tsp for double batch, 2 tsp for triple). Whisk the batter vigorously for 1 minute to aerate. Alternately, use a stand mixer with a fitted whisk attachment and whisk on med-high (6) for 1 minute. Test to see if a drop of batter floats on top of a bowl of water (See Note). If not, whisk again for another minute.
Preheat oil: Heat a medium frying pan or heavy-bottomed pot over medium heat. Add oil so that it’s about 1.5-2”/4-5 cm deep. It should be deep enough so batter doesn’t stick to the to bottom. Once the oil is hot, adjust heat level as needed to maintain medium heat (around 320-340°F/160-171°C).
Prepare Water Bath: Meanwhile, fill a large bowl with lukewarm water and set aside. Line a plate with paper towels.
Fry Bhallas: Gently drop around 1 tbsp of batter into the hot oil. (Cookie scoops work great if you like a round shape!) Fry, turning often, until golden all over, about 10 minutes. You want to ensure they have time to fully cook from the inside.
Transfer to water bath: Using a slotted spoon, remove the bhallas and place them on a plate lined with a paper towel. (See Note 4 for Storing/Freezing) Transfer to the bowl of water and allow them to soak for at least 15-20 minutes. You’ll know they’ve soaked long enough when the color gets lighter and they’ve lost their firmness.
Meanwhile, prepare yogurt: In a medium bowl or large measuring cup, whisk the yogurt, milk, water, sugar, chaat masala, red chili powder, and salt until smooth with no clumps. The consistency should be like a yogurt raita. If needed, thin out with another tablespoon or two of milk or water. Keep in mind it'll thicken when stored in the fridge. Taste and adjust seasoning, adding salt to taste, chaat masala for tang/chatpata, red chili powder for heat, and sugar for sweetness. (I've used base/minimum amounts.)
Squeeze out water: Remove the water from bhallas by placing them between the hollows of your palms/fingers and gently but firmly squeezing the water out. (It’s totally okay if you break some – no one will notice.) Transfer to a deep serving platter. Top with the yogurt, ensuring the bhallas are doused in the yogurt.
Serve: Allow to rest for at least 30 minutes so the bhallas have time to soak in the yogurt. If waiting longer, cover and refrigerate until ready to serve. Top with Imli ki Chutney, Green Chutney, red onions, chaat masala, a dash of red chili powder for color, and optional toppings. Serve cold or at room temperature with toppings on the side.