Heat Oven: Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
Prepare the Topping: Place about a ¼ cup of white sugar in a small bowl. This will be used roll the dough balls in prior to baking. Place to the side. If doing a long fermentation, then do this step prior to baking.
Mix Wet Ingredients: In the stand mixer bowl, combine the peanut butter, softened butter, and brown sugar. Mix until smooth. Add the egg, vanilla extract, and sourdough starter, mixing until well combined.
Add Dry Ingredients: In separate bowl, whisk together the baking soda, salt, and flour. Gradually add the flour mixture to the peanut butter mixture, stirring until just combined. Make sure to scrape down the sides of the bowl. At this point you can do a long fermentation on the dough by placing a piece of plastic wrap over the large bowl and place it into the fridge overnight for 12-24 hours prior to baking. Alternatively you can proceed to baking after mixing the dough.
Shape Cookies: Scoop tablespoon-sized amounts with a cookie scoop or spoon. Roll dough into balls. Then, roll the balls around in white sugar. Place the 1-inch balls on the prepared baking sheet, spacing them a couple of inches apart.
Bake: Bake in the preheated oven for about 10-12 minutes, or until the edges are lightly golden brown.
Prepare the Topping: While the cookies are baking, begin to remove the wrappers from the chocolate kisses.
Add Chocolate Kisses: Remove the cookies from the oven and immediately press a hershey kiss into the center of each cookie. Allow them to cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.
Enjoy: Our favorite way to enjoy these is with a cold glass of milk!
Store: Store in an airtight container.
Enjoy your delicious sourdough peanut butter blossom cookies!