Melt the butter. Sift the flour and a pinch of salt into a bowl, make a well in the middle. Pour the melted butter, the lemon juice and 2 tbsp cold water into the well, and mix to make a firm dough. Knead on a floured surface to make a smooth pastry, wrap and chill. Finely mince the chicken either in a food processor or by chopping on a board. Heat the oil in a large frying pan, add the chicken and sauté over a high heat for 5 mins. Add the onion and garlic and sauté for a further 3-4 mins. Stir in the paprika, chilli, sherry and lemon zest and cook stirring until the liquid has evaporated. Remove from the heat and season to taste. Spread on a plate to quickly cool the mixture. On a floured surface roll out the pastry until 3mm thick, then use a 10cm round cutter to press out 12 rounds, re-rolling as necessary. Heap a tablespoon of the chicken filling over one half of each round. Wet the edges of the rounds with water, then fold the pastry in half to enclose the filling. Crimp the edges with a fork to seal. Heat the oil in deep pan or fryer to 180°C, then add the pastries in batches, turning occasionally until they are golden brown. Cook the chicken through until no pink is showing. Drain on kitchen paper. Serve warm or cold.