In a medium bowl, sift together the flour, cornstarch and salt; set aside. Wash, dry and zest 2 large lemons or about 1 tablespoon plus 1/2 teaspoon lemon zest. In a bowl fit with a paddle mixer, beat the softened butter and powdered sugar for a few minutes until light and fluffy. Reduce the speed and beat in 2 drops yellow food coloring (for color, if desired), lemon zest vanilla extract. Wipe down the sides of the bowl and the beater then continue to beat until everything is mixed and blended. Slowly add in 1/2 cup dry flour mixture at a time, beating on slow until gone. Turn off blender and wipe down side of the bowl with spatula and gently food everything in then run for 30 seconds on low with the mixer again. Cover top with saran wrap and refrigerate for at least 30 minutes to cool dough.
Lay out a long piece of saran wrap. Use a hard spatula to fold dough edges in and gently start forming a long dough roll in your hand then place on saran wrap. Seal saran wrap and roll dough or form it to 10 inches long and about 6 and 3/4 around making sure the ends are patted almost square. Slice cookies; I was able to get about 20 cookies out of the dough.
Preheat oven to 350 degrees F. Bake on a prepared cookie sheet lined with Reynolds® Cookie Baking Sheets for 11-13 minutes. Cookies should not spread in oven. Allow to cool on baking sheet for 20 minutes until cool enough to move.
To make icing, in a small bowl combine powdered sugar and water then mix to incorporate well. Use a spoon or fill a pastry bag with icing and drizzle over cool cookies. Zest lemon and sprinkle over top for more added flavor, which is amazing! Dust with powdered sugar if desired.