Preheat oven to 350°F (177°C). Line a large cookie sheet with parchment paper.
Add sliced almonds to a food processor and pulse until they become the size of large coarse crumbs. See photo in post for reference.
Add egg white and powdered sugar to a large mixing bowl and whisk until smooth. Use 1/3 cup powdered sugar if you prefer less sweet for your cookies. Use 1/2 cup if you prefer sweeter cookies. Add the almonds into the egg mixture. Stir thoroughly until all of the almonds are evenly coated in the egg mixture.
Use a 1.5 tbsp cookie scoop to scoop the mixture, releasing it onto your prepared baking sheet and spacing the scoops about 1.5-2 inches apart. Use the back of a metal spoon to flatten and shape each cookie until it becomes a thin round disk (between 1/8-1/4 inch thick). You can also shape the sides so the cookies are more round. The cookies will not change shape during baking so shape them how you want the final outcome to be. You want to keep the cookies thin so that they crisp up fully.
Bake the cookies for about 20 minutes or until the edges turn deep golden brown and the surface is lightly browned. You do need the surface to be lightly browned in order for the cookies to fully crisp up in the center. If needed, you can rotate your baking pan to help the cookies brown more evenly.
Remove cookies from the oven and allow them to fully cool on the baking sheet. Don't attempt to move them from the baking sheet until they are fully cooled because the cookies need to set. The cookies will continue to firm up as they cool. Once they are fully set and cooled, the best way to remove them is to peel them off the parchment paper instead of using a spatula. Cookies can be eaten after they are fully cooled. Cookies need to be stored in an airtight container soon after they are fully cooled, otherwise they will absorb moisture in the air which can cause them to soften. Store any uneaten cookies in an airtight container for a few days at room temperature.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.