The cookies need to be made thin and small so they may dry properly while baking. A crisp cookie must have a high content of fat and sugar. You must also store them properly in order to keep them crisp. The secret is to use vegetable shortening or lard. These fats will break the dough down into flaky rather than crumble strands.
Most recipes call for a pinch of salt.
Salt brings out the flavor of all the other ingredients. Allow the cookies to cool long enough for their shape to hold. If the cookies are too hot, the dough hasn't had time to set and is still too soft. Be sure to include your name for credit.