Cream butter and sugar until fluffy, preferably with a hand mixer.
Add egg, vanilla, zest and juice and blend until well combined.
Add in flour (by hand or on low speed of mixer) just until well blended.
Chill dough for about 1 hour.
Drop by Tablespoonfuls onto parchment paper lined baking sheet about 2 inches apart.
Bake for 13-15 minutes at 350 degrees or until bottoms and edges are a light golden brown.
Cool on baking sheet for about 5 minutes and then move to cooling rack to complete cooling.
For the Glaze
Blend confectioners sugar, zest and juice until smooth and creamy. Start with 2 Tablespoons of juice and add more if needed to reach desired consistency.
Notes
Let butter come to room temperature before using.
Let egg come to room temperature before using. A cold egg can be placed in bowl of warm water for a few minutes.
Be sure to chill dough before making cookies.
A cookie scoop is recommended for uniform sized cookies.