1. Place the whole blanched almonds and 1/2 cup of the powdered sugar in a large food processor (at least 7 cups in volume) fitted with a steel blade. Process the nuts and sugar until the nuts are very finely ground, stopping periodically to scrape the sides of the processor bowl. The sugar will help prevent the nuts from turning into almond butter, but still be careful about overprocessing.
2. Once the almonds are very finely ground, add the rest of the powdered sugar and pulse until it is completely mixed into the ground almonds.
3. Stop the processor and add the egg white and the almond extract, if using. Turn the processor back on and process the almond paste until it comes together in a clump in the food processor.
4. If it seems very sticky, add a little more powdered sugar, a spoonful at a time, until it is smooth.
5. You can use the almond paste at once or wrap it to use at a later date. Wrap it tightly in plastic wrap and then store it in a zip-top bag. Wrapped this way, the almond paste can be kept for up to 3 months in the refrigerator or 6 months in the freezer. Make sure to bring the almond paste to room temperature before using it in recipes.