Preheat oven to 375F.

Roll out pasty on floured surface to 12 x 9 inch rectangle. Cut pastry in half, lengthwise, creating two 12 X 4 1/2" strips. Place 1 pastry strip on large baking sheet. Spread jam evenly over pastry, leaving 1/2" border on all sides.

Fold remaining pastry strip in half lengthwise. Using small knife and beginning 1/2 inch from one end of pastry, cut slit through fold to within 1/2 inch of unfolded side of pastry. Repeat cutting slits at 1/2 in intervals. Unfold dough and open flat on work surface. Whisk egg and cream in small bowl to blend. Brush cut pastry with some egg mixture. Brush edges of jam covered pastry strip with some of the egg mixture. Place cut pastry strip over strip with jam, egg glazed side up. Press edges firmly to seal.

Bake tart until pastry is golden, about 25 minutes. Transfer sheet to rack and cool 5 minutes. Using a large metal spatula, loosen tart from sheet. Slide tart onto rack and cool completely. Cover and let stand at room temperature.