Preheat oven to 400°F. Line 2 baking sheets with parchment paper; set aside.
In a large bowl, whisk together the flour, Parmesan cheese, sesame seeds, poppy seeds, baking powder, and salt.
Slowly add the warm water and stir with a spatula or wooden spoon.
Add the oil and stir until the dough starts to form a smooth ball. Add more water by the teaspoonful, as needed.
Divide the dough into 2 balls. Using a rolling pin, flatten each ball of dough into a rectangle about 9" x 13"
In a small bowl, whisk the egg white. Then use a pastry brush to brush it over the dough.
In another small bowl, whisk together the Parmesan cheese, sesame seeds, and poppy seeds for the topping. Sprinkle the topping evenly over the dough.
Using a pizza cutter or knife, score the dough to create the cracker shapes. To do this, gently cut 7-8 score lines about 1-inch wide into the top of each rectangle, taking care NOT to cut the entire way through the dough. Then make about 11-12 score lines in the opposite direction, also about 1-inch apart. You should have anywhere from 70 to 80 crackers scored, depending on how thick you roll the dough and size of each cracker.
Bake for 15-18 minutes, or until the crackers are golden brown. Remove from the oven and immediately snap the crackers apart along the scored lines. If you leave them too long they sometimes puff a bit and won't snap along the lines as well.
Place crackers on a rack to cool for 10 minutes.
Notes
Makes approximately 6 to 7 dozen crackers (72-84 crackers).