Cup of Yum
1. Preheat oven to 350F.
2. In KitchenAid mixer or with electric hand-mixer, cream the butter until it is smooth.
3. Add sugar and beat with the butter until well-creamed.
4. Add vanilla extract and salt, stirring until well-combined, pausing occasionally to scrape down the sides of the bowl using a rubber spatula to ensure ingredients are well-incorporated.
5. Add egg yolk and beat until combined.
6. With mixer on medium-low speed, gradually add flour until well-incorporated (you will definitely need to scrape down the sides and the bottom of the bowl several times for this, as the mixture is fairly dry and crumbs tend to settle at the bottom of the bowl) and dough begins to clump together.
7. Transfer dough to clean surface and use your hands to form it into a cohesive ball.
8. Flatten into a disk (about 1" thick), cover with clear wrap, and chill for 10 minutes.
9. Once dough has chilled, transfer it to a clean, lightly floured surface and use a lightly floured rolling pin to roll out to about ¼" thickness.
10. Lightly flour 2 ¼" diameter round cookie cutters and cut out your cookies, transferring them to ungreased cookie sheet.
11. Once you have cut out all of the cookies that you can, be sure to re-combine the scraps and roll out and cut out again to get the maximum number of cookies from your dough.
12. Bake cookies on 350F for 10-12 minutes and allow cookies to cool completely before topping with peanut butter.

Peanut Butter Filling

1. Prepare peanut butter filling by creaming together peanut butter and butter in KitchenAid or with electric hand mixer. Stir in vanilla extract.
2. Gradually add powdered sugar until well-combined, pausing to scrape down sides of bowl.
3. Transfer peanut butter mixture into a Ziploc bag with one corner snipped and pipe peanut butter evenly on top of each cookie (about 1 ½ Tbsp of filling per cookie).
4. Gently spread evenly with a knife so that the filling nearly touches the edges of each cookie.
5. Transfer cookies with peanut butter to freezer and chill for 10-15 minutes while you prepare the chocolate topping.
6. Prep chocolate by placing melting wafers in microwave-safe bowl and microwaving at 15 second increments and stirring in between. Repeat with your dark chocolate chips (if using) in separate, small bowl until melted.
7. Once chocolate is melted, remove cookies from freezer and balance each cookie on the tines of a fork while you pour melted chocolate overtop, until cookies are coated (I do not coat the bottoms of the cookies, I think it makes the chocolate overwhelming to do this).
8. Transfer to cooling rack (place wax paper beneath for easy clean up) and immediately drizzle with dark chocolate. Allow to set and harden before serving (the dark chocolate will take a bit longer to set if you use chocolate chips and not wafers).