Prepare the eggplant: Wash the baingan thoroughly under running water. Pat dry with a kitchen towel. Trim the stem and slice into ½-inch thick rounds. Avoid slicing too thin, as they might burn; too thick, and they won't cook evenly.

Make the spice mix: In a wide bowl, combine turmeric powder, red chili powder, salt, sugar, and rice flour (or atta). Mix well to form a dry marinade. This step infuses the slices with flavor and helps achieve that signature crisp.

Marinate the slices: Add the eggplant slices to the spice bowl. Gently toss or rub the mixture onto both sides of each slice, ensuring even coating. Let it sit for 5-10 minutes. This allows the salt to draw out moisture, preventing sogginess during frying.

Heat the oil: In a heavy-bottomed skillet or kadai, heat mustard oil over medium-high heat until it starts smoking lightly (this removes the raw pungency). Reduce to medium heat.

Fry the baingan: Carefully place 4-5 marinated slices in the hot oil without overcrowding. Fry for 3-4 minutes per side until golden brown and crispy. Use a slotted spoon to flip gently.

Drain and repeat: Remove the fried slices to a paper towel-lined plate to absorb excess oil. Repeat with remaining slices, adding more oil if needed.

Serve hot: Your homemade baingan bhaja is ready! Enjoy immediately for the best texture.