Found on Reddit, a very nice writeup. .
Ingredients
1 kg (2.2 lbs) Potatoes - any variety will be fine but cooking will be easier if they are a similar size
2 medium onions
1 Tbls (generous) black onion seeds
Salt
BLack Pepper (lots of)
3 cloves crushed garlic
1 inch grated ginger
300G (10 oz) mixed frozen vegetables (see note)
3 Tbls Garam Masala
2 Tbls cumin seeds
1-1/2 Tbls lemon juice
450g flour
4 Tbls cornstarch or potato starch
450 ml (1.9 cups) warm water
1.5 l oil (2.6 pints)
Note - this recipe is for vegetable samosas. He used a mix of green beans, carrots, peas and cauliflower but said use whatever mixed vegetables you enjoy most. You must have peas!
Instructions
1. Boil potatoes until done - he recommends not peeling them to prevent them getting watery, which is a problem when frying them. Drain and leave to cool.
2. For pastry, stir together the flour, corn/potato starch, 1.5 TSP salt and onion seeds in a mixing bowl. Drizzle in 3 tbls oil (don't worry about mixing it in). Add enough warm water to make a soft pliable dough, starting with 1 cup and adding an additional tbls as needed. Mix with a spoon and then your hand until no more dry lumps of flour. Try not to "knead" it. Dough should be pliable but not sticky.
3. Peel and finely chop onions. Sautee in 3 tbls oil until soft but not colored. He suggests speeding this up by adding 1 cup water and cooking until the water boils away (and possibly adding a second cup).
4. Peel potatoes and finely chop, the pieces should be about the same size as the vegetable pieces.
5. Add 2 tbls cumin seeds to onions over medium heat and sautee until fragrant (don't let them brown). Add garam masala and plenty of black pepper - you may want to add another tbls of oil to get them to bloom. Cook for about 30 seconds. Add vegetables, breaking up larger pieces like green beans. Add garlic and ginger. You don't need to cook the vegetables, just defrost. Add 2 tsp salt and cook over medium heat until vegetables are warmed and everything is fragrant, about 6 or 7 minutes.
6. Turn off the heat, add the potatoes, and mix well. Mix in the lemon juice. Taste-test for seasoning.
7. Cut off about 1/3 of the pastry dough and form into a cylinder. Cut cylinder into pieces about the size of a ping-pong ball (50 - 60g). With rolling pin, roll into a circle about 15cm circumference and a bit thicker than a quarter (dough will probably stick to rolling pin but it should easily peel off). Put plastic wrap over disks as you roll new ones.
8. When ready to fry, cut each disk in half and bring the straight edges together to form sort of an ice-cream cone shape. Spoon in filling - don't overfill but try and get all the way down to the bottom point of the cone. Firmly press edges to seal.
9. Heat oil for deep frying to about 180C (356F). Carefully lower in about six or so samosas (temperature may drop to 160C or 320F, which is fine). He uses a 24cm (9.5in) dutch oven.
10. Deep fry until golden and crisp, about 5 - 6 minutes, turning over after 3 minutes. Drain on paper towels and serve. These can also be frozen. Defrost in oven and reheat in 180C (356F) oven until heated and crisp, about 15 minutes.