Shortbread
Butter, sugar and flour, and nothing else — no egg, no leavening, no liquid. Which is exactly why the dough has to go into the oven cold and bake at a low temperature: butter and flour are the only things holding it together.
At a glance
Ingredients and method are in the app
Kitchen Pantri holds the full ingredient list and step-by-step method for Shortbread, checks it against what is already in your pantry, and adds anything missing to your shopping list. The app is free to use; you set up a Pantri account when you first open it.