Combine the flour, baking soda, and salt in a medium size mixing bowl and set aside.
In a large mixing bowl beat together the butter, sugar, egg, limoncello, and vanilla extract.
Add the flour mixture to the butter/sugar mixture to form a soft dough.
Roll the dough into small balls and flatten slightly. Place on ungreased cookie sheets. Bake at 375 degrees for 10 minutes.
Cookies can be finished with a limoncello icing glaze as follows:
Combine the 3/4 cup powdered sugar and the 5 teaspoons of limoncello in a small mixing bowl. The glaze consistency should be a little bit on the thin side.
Spread a thin layer of the icing glaze on each cookie. Sprinkle with decorative sugar or a bit of lemon zest if desired.
Note: if you would like a thinner glaze that can be drizzled over the cookies, just add a bit more limoncello to the icing mixture until you have the desired consistency.