Rosie's Lemon Drop Cookies w/white chocolate chips

2 cups butter, softened
1 cup powdered sugar
3 1/2 cups all-purpose flour
1/2 cup cornstarch
2 tablespoons lemon zest (about 3 medium lemons)
1 tablespoon vanilla extract
1  cup white chocolate chips (optional...but very good)


1 cup powdered sugar
2 1/3 tablespoons lemon juice (squeeze from the lemons just zested)
2 teaspoons lemon zest
Directions:

1
Heat the oven to 350°F
2
In large bowl, beat butter and 1 cup powdered sugar with electric mixer on medium speed. Stir in flour, cornstarch, lemon zest and vanilla and white chocolate chips  until well blended.
3
Shape dough into 3/4-inch balls and place about 1 1/2 inches apart on a parchment-lined cookie sheet and flatten a little.
4
Bake 9 to 11 minutes, or until edges are light golden brown. Remove carefully from cookie sheet to wire rack. Cool completely.
5
Whisk together 1 cup powdered sugar, lemon juice, and zest in a small bowl. Stir in additional juice if necessary, or powdered sugar to thicken.
6
Dip the tops of the cooled cookies in icing and place on the parchment paper that you baked the cookies on, to harden.