Make well in the flour. add oil, salt and little water. Mix well till crumbly. Add more water little by little, kneading into soft pliable dough. Cover with moist cloth, keep aside for 15-20 minutes. Beat dough on work surface and knead again. Re-cover.
Heat 3 tablespoon oil, add ginger, green chilli, garlic, coriander seeds. Stir fry for a minute, add onion, saute till light brown. Add coriander, lemon, turmeric, salt, red chilli, garam masala. Stir fry for 2 minutes, add potatoes. Stir further 2 minutes. Cool. Keep aside.
Make a thin 12.5 centimeter / 5 inch diameter round with some dough. Cut into two halves. Run a moist finger along diameter. Join and press together to make a cone. Place a tablespoon of filling in the cone and seal third side as above. Make five to six. Put in hot oil, deep fry on low to medium till light brown. Do not fry on high, or the samosas will turn out oily and soggy.
Drain on rack or kitchen paper. Serve hot with green and tamarind chutneys, or tomato sauce.
There are zillions of variations of this recipe but this one calls for the most mainstream ingredients so should be accessible to all.