Put the potatoes in a large pot of water and bring to a boil. Let the potatoes boil until fork-tender but not too tender that they fall apart. You want a nice structured potato. Drain the potatoes and place under cold running water for a few moments. Once the potatoes are cool enough to handle, cut them into cubes.
Heat the olive oil in a large skillet over medium-high heat. Add the mustard seed and let cook 2 minutes. Add the cumin seeds and curry leaves, if using, and sauté 1 minute. Add the onion and sauté while stirring for a minute. Add the turmeric, sauté, stirring frequently, about 3 minutes, until the onion is translucent. Cover and cook, stirring often, until the onion is golden and caramelized, 7-8 minutes.
Add the potato cubes to the skillet. Mix thoroughly until the potatoes are coated with the spice and onion mixture. Cover and cook for 5 minutes, stirring occasionally to prevent sticking. Add the tomatoes and 1 to 1 1/2 teaspoon sea salt, stir well, and continue cooking, covered, for an additional 5-6 minutes. Add the chili pepper, the garlic-ginger paste, and the garam masala, and stir well. Continue cooking until the potatoes are nice and tender, about 2-3 minutes. Remove to a serving bowl. Garnish with fresh cilantro. Bon appétit!