Preheat oven to 350 degrees. Line a baking sheet with parchment paper or coat with cooking spray.
In a large bowl, using a hand or electric mixer, blend together the egg whites, egg, and oil.
Add the vanilla and sugar and continue to mix well.
Mix in the flour, poppy seeds, baking powder, and salt until the dough is combined. (Do not over mix) Place dough in the refrigerator for 45 minutes to firm up.
Divide the dough into 4 portions. Shape each portion into a loaf 2 ” wide by 1″ high, and about 10″ long. Place the loaves 2 inches apart on the prepared baking sheet.
Bake for 30 minutes until golden brown. Remove from oven and transfer loaves to a cutting board using a spatula. Cut the loaves crosswise into ¼- inch slices. Place the slices back on the baking sheet.
Return the sliced loaves back to the oven and bake for 12 minutes. Turn the biscotti over and bake for another 12 minutes or until crispy.
While still slightly warm, dust both sides of each biscotti with powdered sugar.