Add in egg and mix until combine, then add egg white, lemon extract and vanilla extract and mix until combined. With mixer running, slowly add in dry ingredients and mix just until combined.
Transfer dough to an airtight container and refrigerate 2 hours. Preheat oven to 375ºF during the last 10 minutes of refrigeration.
Bake in preheated oven 9 - 11 minutes. Allow to cool 5 minutes on baking sheet before transferring to a wire rack to cool. Cool completely then frost.
For the Lemon Frosting: Combine all ingredients in a large mixing bowl, using an electric hand mixer, whip until frosting is smooth and fluffy. Mix in food coloring if desired or sprinkle cookies with yellow sprinkles.