Step 1PreparationRoll out and cut dough: Roll out dough on a lightly floured surface, dusting with flour as necessary, into an 18- by 10-inch rectangle. Brush off excess flour with pastry brush and trim edges with a pizza wheel or sharp knife. Cut dough vertically into fourths, then horizontally into fourths to make 16 rectangles.Step 2Form pains au chocolat: Place 2 batons, flat sides together, along a short side of 1 rectangle about 3/4 inch from edge, letting batons extend over sides. Fold bottom edge of dough over batons and roll up dough around chocolate. Place, seam side down, on a parchment-lined large baking sheet.Step 3Make more pastries in same manner, arranging them 2 inches apart on baking sheets.Step 4Let pains au chocolat rise: Slide each baking sheet into a garbage bag, propping up top of bag with inverted glasses to keep it from touching pastries, and tuck open end under baking sheet.Step 5Let pastries rise until slightly puffy and spongy to the touch, 2 to 2 1/2 hours.Step 6Bake pains au chocolat: Adjust oven racks to upper and lower thirds of oven and preheat to 425°F. Remove baking sheets from bags. Spritz inside oven generously with spray bottle and close door. Put pastries in oven, then spritz again before closing door. Reduce temperature to 400°F and bake 10 minutes without opening door.Step 7Switch position of sheets in oven and rotate sheets 180°, then reduce temperature to 375°F and bake until pastries are deep golden, about 10 minutes more.Step 8Cooks' NoteBaked and cooled pains au chocolat keep 1 month: First freeze them, uncovered, on baking sheets until firm, then wrap them snugly in foil before returning to freezer. When ready to serve, remove foil and bake (not thawed) on a baking sheet in a 325°F oven 5 to 10 minutes.