Sometimes a cookie is fabulous just by itself. For example, a great chocolate chip cookie or a chocolate crinkle cookie. Nothing else is needed. Sometimes, though, the cookie needs a little more to give it that umph. Recently I made plain sugar cookies which were pretty good, but when I put two cookies together with frosting in between they moved up to really really good.
Here is the frosting I used:
Frosting for Sugar Cookies, or anything else!
4 cups confectioner's sugar (it is a good idea to sift the sugar if there are any lumps at all)
1/2 cup butter that has been sitting at room temperature until softened
1/2 cup vegetable shortening
1 teaspoon vanilla extract
2-3 Tablespoons of milk
Mix the confectioner's sugar, butter (softened, remember!), vegetable shortening and vanilla in a bowl, adding milk a little at a time until the consistency is just what you want for spreading.
You could probably add another flavoring. Some people like almond flavoring. I like it, too, but have had bad results depending on the almond extract. Some almond extract is very concentrated making icing inedible if you use the same amount as a less fully-flavored extract. If using additional flavorings, be smart and add only a little at a time, tasting to be sure you have not over-done it.