In a medium bowl, combine the flour and salt together.
In a large mixing bowl, beat butter, sugar, lemon zest, and vanilla until light and fluffy with an electric mixer, about 3 minutes. Scrap down the sides occasionally. Add egg yolks and beat until just blend. Add flour mixture and beat just to blend. Divide dough in half. Roll each half into a 8-inch long log (1½-inch diameter). Wrap the dough in plastic wrap and chill in the fridge for at least 1 hour.
Preheat the oven to 350˚F. Arrange racks in lower and upper thirds of the oven.
Line 2 baking sheets with parchment papers. Unwrap 1 dough log. Cut the ends, then cut the log into ¼-inch rounds with a sharp knife. If there are little holes in the middle of a round, patch using the end parts that you cut out. Transfer the rounds to the prepared sheets, spacing 1 inch apart.
Bake until cookies for about 16 – 18 minutes, rotating the baking sheets top to bottom and front to back after 9 minutes. Bake until the cookies are firm and golden grown around edges. Take out the baking sheets and let the cookies cool for 1 minute. Transfer the cookies to cooling racks and let cool completely.
Repeat with the remaining dough log using cooled baking sheets and new parchment papers.
For the icing, whisk sugar and 1½ tablespoon juice in a small bowl. Test the icing thickness with a fork until the icing to reach a drizzling consistency. Add more juice if the icing is too thick. Drizzle the icing over the cookies. Decorate as desired. Let stand until icing sets, about 30 minutes.