preheat the oven to 400°. Line 2 baking sheets with parchment paper. For filling, process ricotta in a food processor fitted with a steel blade for a few seconds until smooth. Transfer to a bowl and mix in the sugar, egg yolks, and vanilla. Mix the flour and cocoa and fold into the mixture. Stir in the raisins and chocolate. Cover and chill in refrigerator for 30 minutes.
Place the pastry on floured work surface. Dust the top with flour and roll out into a 20 x 15" rectangle about 1/4 inch thick. Trim the edges to straighten. Cut the pastry into 12 squares each 5 inches.
Spoon 2 tablespoons of the filling onto the center of each pastry square. Brush the egg around the edges of the pastry and fold one corner diagonally over to meet in the opposite corner. Press down on the pastry, joining the two layers. Place on the prepared baking sheets 1 inch apart. Refrigerate for 15 minutes. Brush the tops with egg and sprinkle with Demerara sugar. Bake until Golden Brown, 25 to 30 minutes. Transfer to a wire rack and let cool. Makes 12 turnovers