Preheat oven to 350 degrees, F. Line 2 half sheet-pans with parchment or Silpat.
In the bowl of a stand mixer, whip whites, granulated sugar and salt to soft peaks. Stop mixer, sift in 10x powdered sugar, and start mixer on low.
When sugar is incorporated, crank it up to high and let whip to very glossy stiff peaks.
Gently but thoroughly fold in the ground nuts. (Grind them in the food processor. They should look kind of like grits when you’re done).
Pipe into the appropriate-sized circles for what you’re trying to do, or spread into half sheet pans with an offset spatula.
Bake for 15-20 minutes until light golden and set, then turn oven down to 275 degrees, and continue to bake until dry and crisp, another 30-45 minutes, depending on the weather.
To test, take them out of the oven and let them sit for 10 minutes to cool some. Then, either gently pick up one of your circles and tap it gently on the bottom, or take a little paring knife and poke a sneaky little hole in the bottom to see if they’re crisp all the way through.
Let cool to room temperature and store wrapped airtight at room temperature if you’re not going to use it/them right away.