Preheat oven to 350 F degrees. Unwrap Hershey's Kisses and set aside.
In a large bowl, beat butter, white sugar, and brown sugar until fluffy.
Add the Greek yogurt and egg and beat until smooth.
In a medium bowl, whisk flour, cocoa powder and baking soda. Stir flour mixture into butter mixture until just incorporated.
Using tablespoonfuls of dough, gently roll cookies into balls and roll in sugar. Place 2 inches apart onto parchment lined baking sheet.
Bake for 8 minutes. Remove from oven and let cool for 1-2 minutes, then place Hershey's Kiss on top, pressing down gently. Do not move the cookies until they are completely cool and the kiss has a chance to set back up (or your little kiss top might flop).
Store cooled cookies in airtight container.
Makes about 3 dozen cookies.