Preheat your oven to 350 degrees F and line two large baking sheets with parchment paper or silpat mats. 

Add the softened butter to the bowl of a stand mixer fitted with the paddle attachment. With the mixer on low speed, slowly add the powdered sugar. 

Once all of the powdered sugar has been added, turn the mixer to medium speed and beat until the mixture becomes light and fluffy — about 1 minute. 

Reduce the speed to low and add the egg and vanilla extract. Scrape down the sides of the bowl, if needed. 

In a small bowl, whisk together the flour, baking powder, and kosher salt. With the mixer still on low speed, slowly add the dry ingredients to the butter mixture. 

Mix just until the cookie dough begins to clump together. You don’t want to overmix! Scrape down the sides of the bowl and mix for another few seconds — just to incorporate any remaining flour and butter. 

Scoop out 18 portions (about 2 tablespoons) and roll them into smooth balls. Place them at least 2 inches apart on the prepared baking sheets. Press the cookies down slightly to form a disc that is about ¼ inch tall. 

Bake for 8 to 10 minutes, or until the cookies are just beginning to brown around the edges. 

Remove the cookies from the oven and press a Hershey Kiss into the top of each one. 

Allow the cookies to cool completely on the tray before storing in an airtight container at room temperature. Cookies will keep for up to 4 days.