1On a lightly floured surface, roll the puff pastry out to a large rectangle or square big enough that the pastry is about 1/4-inch thick.
2Preheat the oven to 375F. Mix together the currants, brown sugar and butter and spread over one half of the pastry. Or mix the butter and sugar, spread it over the pastry and sprinkle with currants. It doesn't much matter.
3Fold the pastry over to cover the filling and roll gently with the rolling pin almost until the currants poke through the surface. Cut into squares or rectangles (any size you like) with a sharp knife and transfer to a parchment-lined baking sheet. Brush with egg, cut a few slits in the top of each with a sharp knife (be careful not to go all the way through) and sprinkle with coarse sugar.
4Bake for about 20 minutes, until golden. Try to share.