1 sheet of frozen puff pastry, thawed but chilled (see thawing directions)
A few tablespoons all-purpose flour
I 4-ounce bar of semisweet chocolate (I recommend Ghirardelli Semisweet Baking Bar) cut into 12 rectangular pieces.
1 egg, beaten with 1 teaspoon water
2–3 tablespoons sugar
Preheat oven to 400ºF. Line a baking sheet with parchment paper. Lightly flour your work surface. Cut your puff pastry, with a sharp knife or pizza cutter, in half lengthwise. Cut each half into sixths, giving you 12 rectangular pieces.
Brush top of dough lightly with egg wash. Place a piece of chocolate in the center of the dough strip. Fold one end over it. Then fold over the other end. Press the seam with the tines of a fork to seal. Add a little extra egg wash to the seam, if it’s not adhering. Repeat with all 12 pieces.
Place the pastries seam side down on the baking sheet. Brush the tops with egg wash. Sprinkle lightly with sugar. Bake for 20 minutes in the center of the oven, until puffed and golden brown. Cool on a wire rack.