Pain au Chocolat

Ingredients

• Croissant dough
• All-purpose flour, for work surface
• 1 large egg
• 1 cup plus 2 tablespoons plus 2 teaspoons chopped semisweet chocolate

Instructions

1. 1
   Place dough on a lightly floured work surface; cover and let stand until butter is slightly softened, 5 to 10 minutes.
2. 2
   Roll dough out to a 10-by-18-inch rectangle. Cut rectangle in half crosswise. Wrap one half with plastic wrap and transfer to refrigerator. Place remaining half on a large (about 18-by-25-inch) piece of parchment paper. Roll into a 16-by-20-inch rectangle, stopping to chill dough as necessary if butter becomes too soft; transfer to a large baking sheet and cover with plastic wrap. Transfer baking sheet to refrigerator and chill until firm, about 30 minutes. Repeat process with remaining piece of dough.
3. 3
   Transfer one piece of dough to a lightly floured work surface so that one of the longer sides is facing you. Halve dough to make two 16-by-10-inch rectangles.
4. 4
   Using a pizza cutter, trim a scant 1/8 inch from all sides of each rectangle of dough. Working quickly, using a pizza cutter, cut each half into seven 3-by-7-inch rectangles. Place 2 teaspoons chocolate in the center of each rectangle, leaving a 1/4-inch border all around. Starting from one short end and working toward the other, roll to enclose. Brush edges with water and gently press to adhere.
5. 5
   Line baking sheets with parchment paper; place 4 rectangles on each prepared baking sheet, seam-side down. In a small bowl, whisk egg with 1 teaspoon water. Brush tops and seams with egg mixture, reserving remaining egg mixture. Place 3 narrow drinking glasses upside-down between each roll of dough; cover well with plastic wrap, making sure plastic does not touch dough. Let stand in a warm place until dough has doubled in size and feels hollow when gently touched, 2 1/2 to 3 hours.
6. 6
   Preheat oven to 425 degrees.
7. 7
   Uncover and remove glasses from baking sheets; gently press down on each roll of dough and brush lightly with remaining egg mixture. Transfer to oven and bake until puffed and golden, about 15 minutes. Transfer to a wire rack to cool. Repeat steps 3 through 7 with remaining piece of dough.