Though there are not many cookie recipes that do not require eggs, any cookies can be turned into eggless cookies by making a few easy substitutions. In most cookies, eggs are used to bind the ingredients together. Eggs are not needed to make the cookies rise, though they do tend to help them expand outward slightly as they bake. This makes it much simpler to make eggless cookies than it is to make eggless cakes or muffins.
One of the traditional types of eggless cookie is called the poor man's cookie. This cookie contains neither milk nor eggs because these are relatively expensive ingredients that many people have been unable to purchase when food has been rationed, such as during war time. Instead of eggs, poor man's cookies use a combination of water, oil, and baking powder that allows the cookies to hold together as they bake. This substitution for eggs, 2 tablespoons (30 mL) of water, 1 tablespoon (15 mL) of oil, and 2 teaspoons (10 mL) of baking powder, can be used in many cookie recipes, though the cookies will often be denser than those made with eggs.
Other eggless cookies can be made just from a combination of flour, sugar, and a fat, such as butter. These cookies are usually flat and dense as they do not rise at all as they are baking. It is also possible to mix other ingredients, such as vanilla or chocolate, into these types of cookies or to top them with a layer of fruit compote, as in the case of lemon squares, though some recipes for these cookies will call for eggs.
It is also possible to make other common types of cookies, including chocolate chip and sugar cookies, without the use of eggs. In order to hold together properly, these eggless cookies will require some sort of egg substitute in order to maintain their texture and density. Egg replacer is one of the best egg substitutes to use in cookies because it mimics to qualities of eggs, helping the cookies to rise and keeping them from breaking apart too easily.
In some eggless cookies, it may also be possible to use bananas instead of eggs. This egg substitute will help keep cookies moist and hold them together as they bake. Eggless cookies that tend to crumble can benefit from the use of binders such as gelatin or xanthan gum.