Cook the potato and carrot in plenty of boiling water for about 12 minutes, until tender but still holding their shape. Drain and set aside. Heat the oil in a frying pan and gently fry the onion for 5 minutes until softened. Add the curry powder and garlic and cook for a further 3 minutes. Now add the drained potato and carrot and the peas. Cook, stirring for about 8 minutes. Add the lemon juice and set aside to cool. Preheat the oven to 180°C, 160°C fan, 350°F, Gas Mark 4. Lay the pastry out on a lightly floured surface. Roll it out a little more so it is slightly larger and thinner. Cut out eight 11cm (4.5 in) diameter rounds with a plain biscuit cutter. Cut each circle in half to form 2 semicircles. Fold each semicircle into an open cone, pressing the edges together firmly. Spoon enough vegetable mixture in to almost fill. Fold the top edges over to seal. Now brush the outside with beaten egg and place on a lined baking sheet. Repeat to make 16 samosas. Bake for 15-20 minutes, until golden brown. Allow to cool a little or eat completely cold, with mango chutney and steamed rice, if liked. Tip: These little samosas are fragrant and delicious but not hot, if you'd like to up the chilli-factor, use a hot curry powder in place of mild and add a pinch of dried chilli flakes with the garlic.