Preheat oven to 350 degrees F.
Combine butter, sugar, brown sugar, egg and limeade concentrate. Beat until creamy.
Add flour, baking soda, cream of tartar and salt. Mix until combined.
Stir in white chocolate pieces.
Place cookies on a parchment lined baking sheet, about 2 inches apart.
Bake for 9-10 minutes or until lightly brown around the edges.
Place cookies on a rack and cool.
Mix together the glaze ingredients until a nice spreading consistency is reached.
Frost cooled cookies.
Sprinkle with lime zest.