Place the potatoes and salt in a large saucepan and add water to cover by 1 inch. Bring to a boil, then reduce to a simmer and cook until the potatoes are tender and a paring knife can be inserted with little resistance, 12 to 15 minutes. Drain the potatoes and set aside to cool slightly.

Heat the oil in a 12-inch nonstick skillet over medium-high heat until shimmering. Add the fennel, cumin, mustard seeds, fenugreek, turmeric, and Kashmiri chili powder and cook until fragrant, about 10 seconds.

Stir in the onion and salt and cook until the onion is softened, 5 to 7 minutes.

Add the garlic and ginger and cook until fragrant. Stir in the cooled potatoes and cook until they begin to brown around the edges, 5 to 7 minutes.

Stir in the peas, then transfer the mixture to a bowl and refrigerate until completely cold, about 1 hour.

Stir the cilantro and lemon juice into the chilled potato mixture and season with salt and pepper to taste.

Pulse the flour and salt in a food processor until combined. Drizzle the yogurt and oil over the flour and process until the mixture resembles coarse cornmeal.

With the machine running, slowly add the water until a dough ball forms. The dough should feel very soft and malleable; if it does not come together, add more water one tablespoon at a time.

Transfer the dough to a floured counter and knead by hand until slightly firm, about 2 minutes. Wrap in plastic and let rest for at least 20 minutes to relax the gluten.

Divide the dough into 12 equal pieces and cover them with greased plastic wrap. Roll each piece into a 5-inch round, then cut each round in half to form 24 half-moons.

Moisten the straight side of a half-moon with a wet finger and fold it in half. Press to seal the seam on the straight side only and crimp with a fork; leave the rounded edge open.

Hold the dough cone in your cupped hand and fill it with the potato mixture, packing it in tightly while leaving a small rim at the top. Moisten the inside rim, pinch the edges together to seal, and crimp with a fork.

Adjust an oven rack to the middle position and heat the oven to 200 degrees. Line a baking sheet with several layers of paper towels.

Heat the frying oil in a large Dutch oven over medium-high heat until it reaches 375 degrees. Fry the samosas in batches until they are golden brown and bubbly, about 3 minutes, adjusting the heat to maintain the temperature.

Transfer the fried samosas to the prepared baking sheet and keep them warm in the oven until ready to serve.