1. Heat oven to 375 degrees F. Unfold 1 pastry sheet. Cut sheet in half across the fold marks. On a lightly floured surface, with a lightly floured rolling pin, gently roll out one half of the pastry into a 14 x 6-inch rectangle.
2. Place rolled-out pastry on ungreased baking sheet. Spread 1/3 cup preserves over top, leaving 1-inch border all around edges. Slice any large apple chunks. Evenly scatter apples over top of preserves. Sprinkle top with half of chocolate bar.
3. Roll other half of pastry into 15 x 7-inch rectangle. Fold pastry lengthwise in half. Along folded edge, cut parallel slits, about 3/4 inch apart and 2-1/2 inches long.
4. Brush border of pastry around filling with some egg. Top with slit pastry; unfold and align edges. Gently press edges together to seal. Brush top with some egg; sprinkle with 1 tablespoon of the sugar crystals.
5. Bake in 375 degrees F oven for 25 minutes or until puffed and golden. Transfer to wire rack.
6. Make second jalousie with remaining pastry, preserves, apples, chocolate, egg and sugar crystals. Bake as above.
7. Serve warm or at room temperature, with whipped cream or ice cream, if desired.