In the bowl of a stand mixer fitted with the paddle attachment, cream butter, sugar and vanilla on medium speed until light and fluffy, about 3-4 minutes. Scrape down sides of the bowl and beat in peanut butter. Again, scrape down sides of the bowl.

With the mixer on low, add in flour and salt. When it's mixed but still crumbly, increase speed slightly and continue beating until dough forms a ball. If the dough doesn't come together, add water, 1 Tbs. at a time, until a ball is formed (I needed 2 Tbs. of water).

Place plastic wrap on counter and turn dough out onto plastic wrap. Shape dough into two logs - either round logs or square logs, depending on the shape you'd like your cookies in. Wrap tightly in plastic wrap and place dough in freezer for 30 minutes.

Just before removing dough from freezer, place two racks in middle and top of the oven. Preheat oven to 350F. Line two baking sheets with parchment paper and set aside.

Slice cookies into 1/3-inch thick slices and arrange on baking sheet, about 1 inch apart from one another (cookies will not spread much). Bake in preheated oven for 10-14 minutes, rotating baking sheets halfway through baking. When starting to brown at edges, remove from oven and allow cookies to cool completely on baking sheets.

When cookies have cooled completely, use a butter knife or offset spatula to spread a heaping teaspoon of peanut butter over each cookie, returning cookie to baking sheet. Place cookies in freezer for 20 minutes, so that peanut butter sets.

Finally, use two forks to dunk each peanut butter-covered cookie in melted chocolate or candy melts. Gently shake off excess chocolate and set back on parchment-covered baking sheet (or an extra piece of parchment or wax paper set on the counter). Sprinkle with sprinkles or sea salt, if using. Allow to sit until chocolate has set. (Candy melts should set fairly quickly. if chocolate is slow to set, you can refrigerate or freeze to help it set.)

Store in an airtight container for 3 days.