Heat 2 tablespoons of vegetable oil in a large skillet over medium heat.
Cook and stir 1 large sliced onion, 4 minced garlic cloves, and 1 tablespoon minced ginger root in the hot oil until golden brown, about 5 minutes.
Stir in 10 minced cilantro sprigs (stems separated), 2 sliced green chile peppers, and 1/2 teaspoon ground turmeric into the mixture.
Mix 1 chopped tomato into the mixture and continue cooking until the tomatoes are softened.
Add 2 peeled, halved, and sliced potatoes; cook and stir until the potatoes are completely coated in the mixture.
Fold in 1 large cut head of cauliflower, season with 1 teaspoon ground cumin, 1 teaspoon ground coriander, 1/2 teaspoon garam masala, 1/2 teaspoon ground red pepper, 1/2 teaspoon white sugar, and salt to taste.
Pour 1/2 cup water over the mixture and stir until evenly mixed.
Bring the mixture to a boil, cover, reduce heat to medium-low, and cook until the potatoes and cauliflower are tender but not mushy, about 20 minutes.
Taste for desired seasoning; if not tart enough, add 2 tablespoons of tomato puree.
Garnish with the remaining cilantro leaves to serve.