Preheat oven to 350°F Spray baking pans with a non-stick spray or line with parchment paper.
Combine flour, sugar and baking powder in a large mixing bowl.
Beat in shortening with mixer on low speed until completely blended into flour. Add the milk, egg and lemon juice, mixing just until blended.
Roll or use a small cookie scoop to get 1-inch cookie dough balls and place 1 inch apart on baking sheet.
Bake 10-12 minutes or until lightly browned. Remove from oven and let set for at least 5 minutes before moving to a cooling rack. Cool completely.
When cookies are completely cool, make the frosting by beating the powdered sugar, butter, 2 tbls of the warmed milk, lemon juice and peel (if using) in a bowl with mixer on low speed until blended. Gradually add in extra warm milk until you get the consistency of the frosting you want.
Spread on top of cookies and let set completely before storing.