Heat 1 tablespoon of vegetable oil in a skillet over medium heat.
Add 2 peeled and quartered onions, cook and stir until soft and translucent, about 5 minutes.
Reduce heat to medium-low, continue cooking and stirring occasionally until onions are golden, about 10 minutes more.
Remove pan from heat, transfer cooked onions to a food processor.
Add 3 quartered tomatoes and 2 small green chile peppers to the food processor.
Grind onions, tomatoes, and green chiles into a smooth paste.
Heat the remaining 2 tablespoons of vegetable oil in the same skillet over medium heat.
Carefully add the onion mixture to the skillet, as it may spatter, and cook for 2 to 3 minutes.
Stir in 2 teaspoons of garlic paste, 2 teaspoons of ginger paste, 2 teaspoons of ground coriander, 1 teaspoon of ground cumin, 1 teaspoon of garam masala, 1/2 teaspoon of ground turmeric, 1/2 teaspoon of cayenne pepper, and salt to taste.
Cook and stir until the oil begins to separate from the mixture, about 5 minutes.
Pour 2 cups of water into the skillet and bring the sauce to a boil.
Add 1 large cooked, peeled, and cut potato to the skillet.
Gently stir in 6 hard-cooked and quartered eggs.
Reduce heat to low and simmer until the sauce has thickened slightly, about 10 minutes.
Remove from heat and garnish with 2 tablespoons of chopped cilantro before serving.