Preheat the oven to 375°F (190°C) and line three baking sheets with parchment paper or silicone mats. (If you need to reuse a baking sheet, make sure you let it come to room temperature first. I like sticking it in the refrigerator for a few minutes to speed up the cooling process.)
In a medium bowl, whisk together the flour, baking soda and salt.
In a large bowl, cream the butter, sugar and peanut butter on high speed until smooth and creamy. Beat in the egg until incorporated, and then mix in the extracts.
Mix in the flour and milk on low speed until just incorporated. Fold in the jimmies, if using. Then scoop 1.5-inch balls of dough and roll each one in the granulated sugar. Place them on the prepared baking sheets, no more than 12 per pan. The dough will be soft.
Use a fork to gently press down the top of each cookie, forming a crisscross pattern. Bake for 8 minutes (one pan at a time).
Take the pan out of the oven and gently press a chocolate kiss on top of each cookie. Let them rest on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. Store in an airtight container and enjoy!