Preheat oven to 350°F. Line a baking sheet with Silpat® Perfect Cookie mat or parchment paper.
In large bowl with an electric mixer, cream butter and 2 cups of granulated sugar until light and fluffy, about 2 minutes.
Add eggs and vanilla and mix until well combined.
In a medium bowl, sift together flour, cocoa powder, baking soda, and salt.
Gradually add the dry ingredients to the butter mixture and mix until combined, scraping down the sides of the bowl as needed.
Cover and refrigerate dough for one hour.
Using a small cookie scoop (about 2 teaspoons), scoop dough into balls, about 1 inch in diameter, and roll in the remaining 1/3 cup of granulated sugar.
Place balls on prepared cookie sheet and bake for 8 to 10 minutes.
If using Hershey’s Mint Truffle Cookies, allow the cookies to cool for 5 minutes before topping each cookie with a kiss. If using Milk Chocolate Kisses, you can top each cookie as soon as they come out of the oven.
I used Hershey’s Special Dark Cocoa Powder, but any unsweetened cocoa will work just fine.
I rolled my dough balls in Chocolate Sugar from King Arthur Flour, but granulated sugar works perfectly.