Melt the butter in a frying pan, then add the onion and cook over a low heat for about 10 minutes until golden and very soft.
Add the sweet potato and paprika then cook, stirring, over a medium heat for 2-3 minutes.
Season and stir in the parsley. Leave to cool for about 5-10 minutes.
Meanwhile, roll out the pastry to 1/4 in thickness, then cut out about 18 rounds, using a 3-4in cutter or upturned cup.
Spoon a little of the filling onto one side of each round and brush the edges with beaten egg. Fold over to form a crescent shape and pinch the edges together firmly.
Place on a non-stick baking sheet, brush with egg and cook for 10-15 minutes, or until well risen and golden. Allow to cool on a wire rack or wrap in baking parchment and a layer of foil to keep warm for the picnic.