Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper or silicone baking mat.
In a large mixing bowl, cream together the peanut butter, softened butter, granulated sugar, and brown sugar until light and fluffy. This can be done using an electric mixer or by hand.
Add the egg, milk, and vanilla extract to the peanut butter mixture. Mix until well combined.
In a separate bowl, whisk together the all-purpose flour, baking soda, and salt.
Gradually add the dry ingredients to the peanut butter mixture, mixing until just combined. Be careful not to overmix as this can result in a tougher cookie.
Shape the dough into 1-inch balls and roll them in additional granulated sugar. This will give the cookies a nice sparkle and a slightly crunchy exterior.
Place the sugar-coated dough balls onto the prepared baking sheet, spacing them about 2 inches apart to allow for spreading.
Bake the cookies in the preheated oven for 8-10 minutes, or until they are set and lightly golden around the edges.
Remove the cookies from the oven and immediately press a Hershey's Kiss into the center of each cookie. The heat from the freshly baked cookies will slightly melt the chocolate, creating the iconic blossom shape.
Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.
Repeat the process with the remaining dough until all the cookies are baked and adorned with a chocolate kiss.
Once the cookies have cooled completely, store them in an airtight container to maintain their freshness. They can be enjoyed for up to a week, although they rarely last that long!