In a large bowl, whisk together 2 cups all purpose flour, 1 teaspoon thyme, and 1 teaspoon salt.
Add ¼ cup ghee (clarified butter) to the flour mixture. Using your fingers, rub the ghee into the flour until the mixture is evenly combined and has a shaggy texture that will hold its shape when pressed.
Add 8–12 tablespoons cold water, one tablespoon at a time, kneading as you add water until you have a fairly stiff dough that does not stick to your hands.
Cover the dough and let it rest for 30 minutes.
While the dough rests, prepare the potatoes: peel 1 lb russet potatoes and cut into 2-inch chunks. Place in a pot of salted water, bring to a boil, and cook until just fork-tender (not mushy). Drain well.
Roughly chop or crumble the drained potatoes; do not mash. Set them aside.
Make the filling: heat 1 tablespoon ghee in a medium pan over medium-high heat. Add 1 teaspoon cumin seeds, 1 teaspoon coriander seeds, and ½ teaspoon fennel seeds and sauté until the seeds begin to sizzle and become fragrant, about 30–60 seconds.
Add 1 tablespoon minced ginger, 1 green chili (diced), and 1 cup green peas. Sauté about 2 minutes, stirring, until the peas are heated through.
Add the chopped potatoes, 1 teaspoon lemon juice, ½ teaspoon turmeric, 1 teaspoon garam masala, 1 teaspoon fennel powder, 1 tablespoon minced cilantro, and salt to taste. Mix gently to combine and sauté for another 1–2 minutes to blend flavors.
Transfer the filling to a bowl and let it cool to near room temperature before assembling.
Divide the rested dough into six equal portions and form each into a ball. Cover the balls and let them rest for about 10 minutes.
Working with one ball at a time, roll each ball into a flat disk about 7 inches across. You may press or roll between two pieces of parchment paper to keep the surface smooth. Keep the other dough balls covered so they do not dry out.
Cut each 7-inch round in half. Moisten the straight (flat) edge of one half with a little water, then fold and press the moistened edges together to form a cone with an open top.
Fill each cone with about 2 tablespoons of the potato-pea filling, gently pack the filling down, then moisten the inside edge of the open side and press to seal the samosa. Repeat for the other half-rounds to make 12 samosas.
Heat about 2 inches of oil for frying in a large, heavy-bottom pan over medium heat. Test the oil by inserting a wooden skewer or toothpick — it should sizzle and produce steady small bubbles.
Fry the samosas in batches, leaving space between them so they do not touch. Fry until golden and crispy, turning as needed (about 1 minute per side as a guideline), adjusting heat so they brown evenly without developing dark brown spots.
Remove fried samosas with a slotted spoon and drain on a paper towel-lined plate.
Serve the samosas warm. (Yield: 12 samosas.)