In a medium bowl, mix flour and salt. Set aside.
In a large bowl, using an electric mixer, beat butter and granulated sugar on medium speed until light and fluffy. This should take about 3 to 5 minutes.
Add the egg, egg yolk, lemon zest, lemon juice, lemon extract, vanilla extract, and a few drops of food coloring, if using. Mix well until combined.
Gradually beat in the flour mixture on low speed until just combined. Be careful not to overmix; you want the dough to come together without becoming tough.
Divide the dough in half and shape each half into a log about 9 inches long and 1.5 to 2 inches in diameter. Wrap in wax paper and refrigerate for 1 hour or until firm.
Preheat your oven to 350°F (175°C).
Slice the chilled dough into 1/4-inch thick rounds and arrange them on ungreased baking sheets lined with parchment paper.
Bake for 12 to 15 minutes or until very lightly browned on the edges. Keep an eye on them to avoid overbaking; you want them to remain soft.
Cool on the baking sheets for 1 minute, then transfer the cookies to wire racks to cool completely.
In a medium bowl, mix powdered sugar and lemon juice until smooth. Adjust the consistency as needed.
Dip the bottom (or top, if desired) of each cookie into the glaze, then gently set the cookies with the glaze side up on a wire rack to allow the glaze to set.