Preheat the oven to 475°. Lightly oil 3 large baking sheets. In a small bowl, combine the poppy seeds and sesame seeds. Transfer the dough to a lightly floured surface and shape into a log. Cut the dough into 6 equal pieces. Working with 1 piece at a time and keeping the rest covered and refrigerated, on a lightly floured work surface, roll out the dough round to a 14-by-9-inch rectangle; if the dough seems too elastic, let it relax for a minute. Transfer the rectangle to an oiled baking sheet, brush lightly with the beaten egg and sprinkle with 1 1/2 teaspoons of the seeds.