1 quantity croissant dough, see Croissant
7oz (200g) dark chocolate
1 large egg, beaten
Divide the dough into 4 equal pieces and roll each out into a rectangle, about 4 × 16in (10 × 40cm). Cut each piece in half, to give 8 rectangles approximately 4 × 8in (10 × 20cm).
Cut the chocolate into 16 even-sized pieces. If you buy two 4oz (115g) bars, they normally divide naturally into 8 pieces each. Mark each piece of pastry along the long edge at one-third and two-thirds.
Put a piece of chocolate at the one-third mark, and fold the short end of the dough over it to the two-thirds mark. Now place a second piece of chocolate on top of the folded edge at the two-thirds mark, brush the dough next to it with beaten egg, and fold the other side of the dough into the center, making a three-layered parcel with pieces of chocolate tucked in on either side. Seal all the edges together to prevent the chocolate from oozing out while cooking.
Line a baking sheet with parchment paper, place the pastries on it, cover, and leave to rise in a warm place for 1 hour, until puffed up and soft. Preheat the oven to 425°F. Brush the pastries with beaten egg and bake in the oven for 10 minutes, then reduce the oven temperature to 375°F. Bake for another 5–10 minutes, or until golden brown.
Formulation courtesy of "Illustrated Step-By-Step Baking"