Preheat oven to 375 degrees F. Line two baking sheets with silicone baking mats or parchment paper.
In a small bowl, whisk together the flour, baking soda and salt; set aside.
With an electric mixer, beat the peanut butter and shortening on medium speed until well blended, about 2 minutes. Add the granulated sugar and brown sugar, and beat until fluffy. Add the egg, milk and vanilla extract, and beat well. Reduce the mixer speed to low and gradually beat the flour into peanut butter mixture until just combined.
Shape dough into 1-inch balls (about 1 tablespoon or dough or a small cookie scoop) and roll in granulated sugar to coat. Place on the prepared baking sheets about 2 inches apart.
Bake for 8 to 10 minutes, or until lightly browned. Remove from the oven and immediately press a chocolate kiss into the center of each cookie (the cookie will crack around edges). Allow to cool for about 5 minutes, then remove the cookies to a wire rack to cool completely. The cookies can be stored in an airtight container at room temperature for up to 1 week.
Notes
You can make these with butter instead of shortening by using the same amount of room temperature unsalted butter in place of the shortening. The shortening helps keep the cookies soft and maintain their shape (not spread), so if you use butter, I urge you to chill the dough for 30 minutes to 1 hour prior to scooping and rolling them into balls.
You can replace the peanut butter with other nut butters, such as almond butter, cashew butter, or even Sunbutter. The taste and texture will be slightly altered, but the cookies will still work.
Whether using peanut butter or a substitute, I recommend the "processed" versions that do not have oil separation and require stirring to keep the cooking from spreading.
In place of the Hershey's kisses, other candies can be substituted, such as Rolos, caramels, chocolate hearts, etc.
You can freeze peanut butter blossoms in an airtight container for up to 3 months.