Cook the potatoes with salt and water for 5 minutes. Add the peas and cook until the potato is tender. Drain well.
Heat the oil in a frying pan. Add the onions, potato-pea mixture, ginger, garlic and masala and fry for 2 minutes. Stir in the lemon juice and cook for 2 minutes. Remove from heat. Slightly mash the potato and peas. Then add the cashews, mix well and season with salt.
Put the flour in a bowl and mix the butter evenly. Add milk to form a dough. Press lightly and divide it into 6 portions. Form each into a ball and roll into a thin chapati or rounds adding flour lightly. Cut each one in half.
Divide the filling equally between each semi-circle of the chapati. Brush the edges all the way round with water and fold over to form triangular shapes, sealing the edges well together to enclose the filling completely.
Heat oil in a pan and fry the samosas until golden golden. Serve hot with chutney or ketchup.