Mix softened butter, salt and 10x and any addition you choose (no more than 1 tablespoon) together until creamy.
Beat in egg whites until smooth, then mix in the flour.
With an offset spatula, spread very thinly onto silpat lined baking sheets, either using a stencil or free form. Make sure it's really thin. You'll only need maybe a teaspoon of batter per cookie, and you should just about be able to see the weave of the silpat under the batter.
Sprinkle nuts on, if using Bake at 350 degrees, F, until lightly golden.
Remove from oven.
If you're leaving them flat, carefully remove silpat from pan and let cool flat on a table or cooling rack.
If shaping, let firm up for a minute, then carefully slide a small offset spatula under them and shape over a rolling pin or spiral loosely around the handle of a wooden spoon. Drape large circles over small inverted cups. Use your imagination.
Notes
By the way, there is no reason in the world why you can't cut out a template in a cool shape and spread the tuile batter into the template. You don't have to make them look like roof tiles. Add any sort of spicing, zest, or herbs that will go well with whatever you're plating. You have my permission to Go Wild with these.