Use a fork to pierce the skin of the potato all over. Microwave for 3 minutes, turn and microwave for another 3 minutes. The potato should feel tender when a fork is inserted. Remove and set aside to cool. When the potato is cool enough to handle, peel and mash. You will need 1 cup (270 grams) of potato.
To a non-stick sauté pan, add the oil over medium heat. When it starts to ripple add the peas, garlic, ginger, cumin, coriander, garam masala and salt. Toss to mix and cook for 1 minute. Add the mashed potato and mix well. Remove from the heat and allow to cool.
Divide the dough into 4 equal parts. Roll each into a ball. Take 1 ball (cover the rest so they don’t dry out) and roll out to a 6-inch (15 cm) circle. You should not need any flour for this. Cut the circle in half.
Take one of the halves and make a cone by taking the two ends of the cut side folding them into the center of the curve so the center of the cut side makes the point of the curve. Wet the edges with water using your finger and press the edges firmly together making sure they are well sealed. Don’t be afraid to manipulate the dough and shape.
Place the 'cone' between your thumb and first finger. Fill with 1 tablespoon of the potato mix. Wet the open edge and pinch together to seal and fold twist on itself to finish the triangle shape. You can see a demo of this in the video.
Repeat until all the samosas are made.
Heat the oil in a high sided pan to 350°F/176°C or when the handle of a wooden spoon is put in the oil it sizzles. Working in batches of 4, fry the samosas until golden brown, about 4-5 minutes, turn and repeat, drain on a paper towel.
Serve warm with the mango sauce.