Combine flour and salt in a large mixing bowl. Stir in vegetable oil until the mixture resembles crumbs. Gradually add water and mix until a soft dough forms. Shape into a ball, cover with a damp kitchen towel, and let rest for 30 minutes.

Place chopped potatoes in a saucepan and cover with about 1 inch of water. Cook until tender, then drain and mash roughly with a fork.

Return the saucepan to medium heat and melt butter. Add chopped onion and ½ teaspoon salt. Cook for about 6 minutes until soft and lightly golden.

Add jalapeño and ginger and cook for another minute. Stir in cumin seeds, garam masala, turmeric, and cayenne. Cook briefly until fragrant. Add mashed potatoes, remaining salt, frozen peas, and cilantro. Mix well and transfer to the refrigerator to cool.

Divide the dough into 6 equal pieces and roll each into a ball. Roll each ball into a thin circle, then cut in half to create two semicircles.

Take one semicircle, brush the edges with water, and fold into a cone shape. Press the edges to seal. Fill the cone with about 2 tablespoons of potato filling and pinch the top to seal. Place on a cutting board so the base flattens slightly. Repeat with the remaining dough to form 12 Potato Samosas.

Heat oil in a deep saucepan or Dutch oven to a depth of about 3 inches. When the oil reaches around 200°F, fry the Potato Samosas in batches for about 15 minutes until lightly golden.

Increase the heat and cook for an additional 5 minutes until deep golden brown and crispy. Remove using a slotted spoon and drain on paper towels.