Cream the butter and sugar, then add the rest of the cookie ingredients and mix well. It will be a thick dough.
Roll the dough into small balls, the place on a cookie sheet.
Use a glass to flatten the cookies.
Bake at 350 degrees for 10-12 minutes, or until the tops start to crack. Edges could be slightly browned, but they won't necessarily be. Let cool completely before frosting.
Frosting
Beat the butter, lime juice, and lime zest until creamy, then add the powdered sugar and mix well.
Add the milk a little at a time until you get a smooth and creamy consistency. Add dash of salt to taste.
Frost cooled cookies, and sprinkle with lime zest.
Notes
*You can make this into any kind of citrus cookie...just replace the lime with lemon or even orange!