Heat oven to 350°F. In mixing bowl, beat together cookie dough and melted chocolate until well combined. With mixer on low, beat in flour. Using a small cookie scoop (about 1 tablespoon), scoop dough out and roll by hand into balls. Place on baking sheet 2 inches apart. Make a thumbprint in each cookie. Sprinkle with crystal sugar. Bake 18 to 22 minutes, until set.
As soon as the cookies come out of the oven, place a chocolate kiss in the center of each. Cool 5 minutes on baking sheet; transfer to cooling rack and cool completely.