Wash, peel, and quarter potatoes, then boil in salted water for 15-20 minutes until fork-tender. Drain and steam dry for 3-5 minutes, then roughly mash with small lumps remaining.
Heat oil in a skillet over medium heat. Add cumin seeds and sizzle for 30-45 seconds until fragrant. Add ginger and green chilies, stir-fry for 1 minute. Add peas and cook for 2-3 minutes.
Reduce heat to low, add mashed potatoes and mix gently. Sprinkle with garam masala, coriander, turmeric, chili powder, and amchur. Add salt to taste and stir in cilantro. Remove from heat and cool completely.
In a large bowl, combine flour, ajwain seeds, and salt. Rub in ghee with your fingertips for 3-5 minutes until mixture resembles breadcrumbs. Add cold water gradually and bring together into a firm, smooth dough. Rest for 30 minutes.
Mix 2 tablespoons flour with 2 tablespoons water to make a thick sealing paste. Divide dough into 7 balls, roll each into a thin 6-7 inch circle, and cut each circle in half to make 14 semicircles.
Take a semicircle, apply flour paste along the straight edge, fold to form a cone, and seal. Fill with 2-3 tablespoons of cooled potato mixture, seal the top opening firmly, and crimp the edge.
Heat oil to 300-320°F (150-160°C). Fry 3-4 samosas at a time for 12-15 minutes until pale golden, then increase heat and fry 3-5 more minutes until deep golden brown. Drain on paper towels and serve hot.