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 and beat until smooth. Add the flour mixture in three separate additions, beating after each until fully incorporated. Cover and refrigerate dough for at least one hour.
Preheat oven to 350 F. Place sanding sugar into a shallow dish. Roll cookie dough into balls and roll each into the sanding sugar. Place cookie dough 2-inches apart onto ungreased baking sheets. Bake for 10-12 minutes. Remove from oven and place one chocolate kiss in the center of each cookie.
