On a lightly floured surface, roll out the pastry dough to form a 28-by-10-inch rectangle, about ¼-inch thick. Place the dough on a baking sheet. Cover with waxed paper and refrigerate while you prepare the plums.

Preheat the oven to 400°.

Cut the plums in half, remove the pits, and cut each half into quarters. Toss the plums with the lemon zest. Starting at the center and working out to within 1 inch of the sides , arrange the plums on the pie dough, slightly overlapping the pieces. Roll in the edges of the dough to meet the plums.

Dust with the sugar and bake for 30 to 40 minutes, or until the outer crust is crisp and golden.

In a small saucepan, melt the jam over moderate heat and brush the top of the tart with the jam.

Slice the tart into the strips and serve warm.