In a medium bowl, whisk together flour, salt and baking soda. In a large bowl using either a hand or stand mixer, beat softened butter with granulated sugar until fluffy.
Add in egg and vanilla extract, beat until smooth. Add the flour mixture in three separate additions, beating after each until all of the flour is incorporated. Add in green food coloring and mix until fully green. Cover and refrigerate cookie dough for at least one hour.
Preheat oven to 350 F. Place powdered sugar into a shallow dish. Roll cookie dough into balls and fully coat in the powdered sugar. Place cookies onto ungreased baking sheets 2-inches apart. Bake for 10-12 minutes.
