the butter in a saute pan. Add the apples
, cover and cook for 10 minutes. Take off the lid, sprinkle over the granulated sugar
, toss in the raisins
, if using, and cook until the sugar caramelizes and coats the fruit (by now possibly a shaggy, golden mass, depending on the type of apples). Taste. Depending on the sweetness of the fruit, you may want a squirt of lemon for balance.
Roll the pastry out to a large square, about 1/4-inch/5 mm thick. Cut into 4 squares, then roll each one to make it slightly rectangular (not that shape matters one bit). Spoon the fruit mixture over half of each pastry, leaving a 1 cm/5 mm margin. Brush the margins with the egg wash
. Fold the pastry over the filling and press the edges to seal. Set on a damp baking sheet. Slash the top of each pastry with a knife. Brush with more egg wash and let rest in the refrigerator for 15 minutes.
Preheat the oven to 425 degrees F/220 degrees C.
Bake the pastries for 10 minutes. Lower the oven temperature to 375 degrees F/190 degrees C and continue baking until golden, puffed up and brown, 10 to 15 minutes longer. Cool slightly on a wire rack and serve dusted with confectioners' sugar.