Butter Cookies: In the bowl of your electric mixer, or with a hand mixer, cream the butter and sugar until light and fluffy.  Beat in the egg, lemon zest, and vanilla extract. 

In a separate bowl, whisk together the flour and salt. Gradually add the flour mixture to the creamed mixture and beat just until incorporated. Scrape down the sides of the bowl as needed. Divide the dough in half and shape each half into a log (round or square) that is about 1 1/2 inches (4 cm) in diameter. Wrap each log in plastic wrap and place in the refrigerator until firm (at least two hours or overnight). Once the log is firm, with a sharp knife, slice cookies about 1/4 inch (.5 cm) thick. (Can also place the logs in the freezer for up to two months. You can then make cookies on demand by removing log from freezer and slicing off as many cookies as you like. Return the log to the freezer.)

Preheat oven to 350 degrees F (177 degrees C). Place oven rack in the center of the oven. Line a baking sheet with parchment paper. 

Place the cookies on the baking sheet, spacing about 2 inches (5 cm) apart. Sprinkle a little granulated white sugar on each cookie before baking. Bake the cookies for about 10 minutes, or until the edges of the cookies are golden brown. Remove from oven and place on a wire rack to cool. Can frost with Confectioners Frosting.

Frosting: In the bowl of your electric mixer, or with a hand mixer, cream the butter and shortening until smooth and well blended. Beat in the vanilla extract. With the mixer on low speed, gradually beat in the sugar. Scrape down the sides of the bowl. Add the milk and beat on high speed until frosting is light and fluffy (about 3-4 minutes). Add more milk or sugar, if needed, until you have the right spreading consistency. Tint portions of frosting with desired food color (I use the paste food coloring that is available at cake decorating stores and party stores).

Makes about 48 cookies.